Kolek undergoes Tommy John surgery

Two weeks ago, Tyler Kolek was working on being effortless on the mound. Now it's going to take a lot of effort to return to the bump.

The Marlins' top prospect underwent Tommy John surgery on Wednesday, according to MLB.com's Jonathan Mayo. He's expected to be sidelined for about a year.

Kolek hurt his pitching arm on March 25 and was bothered by elbow discomfort after that. The right-hander had an MRI, was examined by team doctors and got a third opinion before deciding on the surgery.

Miami made Kolek the second overall pick in the 2014 Draft and has patiently watched him grow since. Last season, the 20-year-old went 4-10 with a 4.56 ERA, 81 strikeouts and 61 walks in 108 2/3 innings over 25 starts with Class A Greensboro.

"He's throwing strikes now, just working at the bottom of the zone," Marlins vice president of player development Marc DelPiano said prior to the injury. "I think all of it's been just energy-related, so he's kind of modified his energy. He's not as high-effort, he's more effortless in how he approaches things with his delivery and his release. I think we've seen semblances of a good fastball right now. He's throwing what looks to be a short slider and it's been effective. He's really thrown a lot of strikes this spring."

Over two seasons, Kolek notched a 4.55 ERA with 99 strikeouts and 74 walks in 130 2/3 innings of 34 games -- 33 of which were starts.