Michael Kopech (White Sox), Luis Urias (Padres), Danny Jansen (Blue Jays), Kolby Allard (Braves), Dakota Hudson (Cardinals)
More than likely
Victor Robles, outfielder, Nationals: Robles came up as part of last year's September roster expansion, so there's no reason to think he won't do the same this time around, even if the Nats aren't in a competitive position. With Bryce Harper hitting free agency this offseason, MLB.com's No. 5 overall prospect will use whatever playing time he can get to show that he's capable of taking over an outfield spot long-term starting Opening Day 2019, especially now that his elbow injury is past him. When healthy, Robles has a chance to be a five-tool star, and he'd make for a promising young tandem with Rookie of the Year candidate Juan Soto.
Kyle Tucker, outfielder, Astros: Ignore Tucker's Major League stats. They came over small samples and with inconsistent playing time. Pay much more attention to his .455/.500/.924 line and 10 homers in 15 games with Triple-A Fresno this month. The 21-year-old, left-handed slugger is a multi-tool offensive threat with 24 homers and 20 steals with the Grizzlies and is undoubtedly Major League-ready. Whenever he jumps to Houston, whether that be Saturday or after Fresno's run through the Pacific Coast League postseason, Tucker should be playing for a spot on the big league playoff roster come October.
Francisco Mejia, catcher, Padres: Mejia already has 12 games of Major League experience, but each of the dozen came with Cleveland, before the deadline deal that sent him to San Diego. The Padres picked him up for relievers Brad Hand and Adam Cimber to be their catcher of the future, and that future should come with the flip of the calendar, even if Austin Hedges is the superior receiver. Mejia has hit .296/.339/.500 with 12 extra-base hits in 28 games with Triple-A El Paso, showing off the offensive potential that makes him MLB.com's top catching prospect. With both he and Urias in the Majors, San Diego fans will be getting a taste of the bright days ahead at Petco Park.
Alex Verdugo, outfielder, Dodgers: In a different world, Verdugo, who has hit .321 with an .842 OPS over 208 career games at Triple-A, would have graduated from prospect status already, having gotten ample Major League time this summer. Instead, he's been stuck behind others on the Dodgers depth chart, coming up only twice this season for 56 total plate appearances. (He's hit .280/.345/.440 with a homer and five doubles in those 56 plate appearances.) Without the 25-man roster limitations, he'll be back with Los Angeles to help the Dodgers chase either an NL West title or a Wild Card spot. Even if he's used as a left-handed pinch-hitter/late-game defensive replacement with a plus arm, Verdugo should make the Dodgers better in the weeks to come.
Willie Calhoun, outfielder, Rangers: Think back to March, when it was a surprise that Calhoun didn't crack Texas' Opening Day roster. Five months later, he remains a prospect, having found his second trip to the Pacific Coast League (.297/.352/.436, nine homers for Triple-A Round Rock) a little more difficult than his first. With Joey Gallo, Shin-Soo Choo and Adrian Beltre covering left field or DH duties in Arlington, it'll be hard for Calhoun to find at-bats, but the non-contending Rangers will try to evaluate what the 23-year-old can bring to the table for their 2019 plans and beyond.
Luiz Gohara, left-hander, Braves: Injuries and ineffectiveness at Triple-A have seen other prime prospects pass Gohara by in the pecking order in his second season in the Braves system, but, when healthy, the 22-year-old southpaw can still sit in the mid-90s and show a plus slider. Eight of his nine Major League appearances have come in relief roles this season, and with the stuff he has, Atlanta could certainly use him in the bullpen again as it tries to hold off Philadelphia in the NL East.
Jonathan Loaisiga, right-hander, Yankees: Having pitched only 2 1/3 innings at Class A or above entering the season, Loaisiga has enjoyed a breakout 2018 that's already included four Major League starts, during which he posted a 3.00 ERA and struck out 21 over 18 innings. The 23-year-old right-hander experienced shoulder issues that kept him out for a good chunk of the summer, but he's returned with three starts over the last two weeks with Double-A Trenton. He could either get spot starts in the Bronx next month or be used as a long man out of the bullpen, thanks to his three above-average pitches and impressive control.
Touki Toussaint, right-hander, Braves: It's difficult to fathom a more successful 2018 for Atlanta's No. 7 prospect. Toussaint continued to show special stuff with his mid-90s fastball and impressive curve, and he improved his once-shaky control to the point where the Braves felt comfortable giving him his Major League debut on Aug. 13. He gave up only earned run in six innings that day and has been dominant ever since returning to the Gwinnett rotation, with a 0.47 ERA, 24 strikeouts and four walks in his last three starts (19 innings). While others could move to relief, Toussaint looks like a pitcher who should get more Major League starts when rosters expand.
Anthony Alford, outfielder, Blue Jays: It's been a bit of a lost season for Alford, who began 2018 on the disabled list with a hamstring strain and has hit just .235/.307/.341 in 101 games at Triple-A Buffalo. He did receive a Major League promotion in early May for nine days but hasn't been back since. That said, he's still got plus-plus speed that make him an asset in the outfield and on the basepaths, so he'd be of value to a Toronto club that should spend September in evaluation mode.
There's a chance
Eloy Jimenez, outfielder, White Sox: Imagine several praying hands emojis here. MLB.com's No. 3 overall prospect has little left to prove in the Minors. He knows it, too, writing as much in a piece for The Players' Tribune. He's hitting .365/.407/.615 with 12 homers in 57 games with Triple-A Charlotte. The White Sox showed they're willing to reward top prospects who perform in the International League when they promoted Kopech, and even if the right-hander had more Triple-A experience, Jimenez, who is already on the 40-man roster, should be handled in a similar way. The only thing holding him back would be Chicago's attempt to delay his service-time clock, even if it can't be explicit about that reason. But a first taste of the Majors now could not only keep Jimenez happy but prepare him for a longer look in 2019.
Jesus Luzardo, left-hander, Athletics: Oakland general manager David Forst was rather blunt this week about whether the A's had any plans to call up Luzardo in September, telling Susan Slusser of the San Francisco Chronicle: "No." Of course, plans can always change. Slusser also notes that Luzardo, who started the season with Class A Advanced Stockton and has climbed all the way to Triple-A Nashville, has 10 2/3 innings remaining before he hits his 120-inning limit for the season. Luzardo hasn't pitched since last week but is by all indications healthy. The A's, who have surprised many by competing in both the AL West and Wild Card races, could be saving his bullets for a Major League bullpen role, and with his plus fastball and changeup and above-average curve, Luzardo could handle such duty right away. Forst seemed pretty straightforward, but this might not be a fully settled case until either the season is over or Luzardo hits those 120 innings, whichever comes first.
Kyle Wright, right-hander, Braves: By comparison, the Braves seem to be broadcasting this one pretty clearly. Atlanta moved its 2017 first-rounder and No. 2 prospect into a relief role for Gwinnett last weekend and has seen positive results so far. Wright has struck out two and allowed two hits over two scoreless innings out of the Stripers bullpen. While this could be in part an innings-saving maneuver, Wright's 137 total frames in the Minors this season are only a slight bump above the 120 he threw between Vanderbilt and the Braves system last spring and summer. This would seem to be more about getting the 22-year-old's plus pitches (fastball, curve, slider) into a position to help the big club, and with Allard and Toussaint already pushing for starts, positions in the Braves rotation are limited. As with the A's and Luzardo, the Braves might decide it's not worth burning a 40-man roster spot for Wright this early, but with the way they've really pushed the envelope with their prospects this summer, Wright would be a logical candidate to join the fight.
Austin Riley, third baseman, Braves: That last sentence goes for Riley, too. After missing about a month with a knee injury in the middle of the season, the Braves' No. 4 prospect has been on a bit of a tear in August, hitting .295/.345/.590 with seven homers and 10 doubles over 27 games. This is as close to Major League-ready as he's looked. However, like Wright, he's not Rule 5-eligible this offseason, so the Braves don't need to rush him onto the 40-man roster. And as good as he's been, he hasn't been good enough for long enough at Triple-A to unseat Johan Camargo at third base right away. Riley would no doubt be a solid right-handed bat off the bench for Atlanta, but he might not be a perfect fit just yet.
Justus Sheffield, left-hander, Yankees: The Yanks have been pretty clear that Sheffield's move to the bullpen in late August was done with an eye on promoting him to the Majors. In fact, manager Aaron Boone even told reporters that he hopes to see the southpaw down the stretch. With the 22-year-old in need of 40-man roster protection this offseason anyway, such a move would make sense. It also helps that New York's top prospect has two plus pitches in his fastball and slider and another above-average offering in a changeup, with all three playing up in shorter stints. That said, Sheffield isn't in the "More than likely" category here because he still has to perform as a Triple-A reliever before the Yankees decide to give him the chance in the Majors, especially if they have any hope of catching the Red Sox in the AL East. Sheffield allowed an earned run over two innings in each of his first two relief appearances but was scoreless for a frame in his third. With Scranton/Wilkes-Barre fighting for its own playoff spot in the International League, he might need a few more positive outings at Triple-A to convince the Yankees he's ready for the jump before moving back to a starting role next spring.
Don't hold your breath
Vladimir Guerrero Jr., third baseman, Blue Jays: Sigh.
Peter Alonso, first baseman, Mets: Mets fans don't need this relitigated, but for the uninitiated: the parent club made it clear this week that they will not be calling up MLB.com's No. 61 overall prospect, despite the fact he's hit 33 homers and produced a .957 OPS between Triple-A Las Vegas and Double-A Binghamton this season. The playing time at first base just isn't there, with Jay Bruce, Wilmer Flores and Dominic Smith expected to get time at the position in the month ahead. Instead, Alonso is slated to head to the Arizona Fall League, where working on his defense will be a priority, because it's clear his bat is ready.
Brendan Rodgers, infielder, Rockies: The Rockies are right in the thick of it with the Dodgers and D-backs in the NL West, and their top prospect just so happens to be at Triple-A Albuquerque. Sounds like a good time to get some reinforcements, right? Well, not so much. Rodgers has played only 17 games in the PCL and is off to a rough start, hitting .206/.242/.254 with no homers. He also missed some brief time with a hamstring injury. Without the need for a 40-man roster add this winter, MLB.com's No. 6 overall prospect will next be tested in the Fall League instead.