Daulton Jefferies slipped out of the first round of the 2016 Draft due to a shoulder injury that cost him a sizeable chunk of his final season at California.
A year later, he's headed to the shelf for the rest of his first full professional campaign.
The Athletics No. 8 prospect will undergo season-ending Tommy John surgery, the team said Thursday. Jefferies has made just seven total Minor League appearances, including two this year.
Jefferies started eight games for the Golden Bears in his junior season, then dominated last spring by going 7-0 with a 1.08 ERA, a 0.84 WHIP and 53 strikeouts while walking only eight in 50 innings.
That was enough for Oakland to select the right-hander 37th overall. The A's sent Jefferies to the Rookie-level Arizona League last year where he didn't record a decision but posted a 2.38 ERA in five starts, striking out 17 and walking only two in 11 1/3 innings.
This season, Jefferies was assigned to Class A Advanced Stockton out of Spring Training. The 21-year-old went four innings in his only start on April 9 vs. Rancho Cucamonga, allowing two hits and striking out two. Four days later, he came out of the bullpen and surrendered six runs -- two earned -- on five hits and a walk while fanning four over three innings.
Oakland general manager David Forst confirmed Jefferies would need surgery but did not say who would perform it, according to MLB.com.