Rockies reliever Jairo Diaz is set to undergo Tommy John surgery after suffering a partial UCL tear, MLB.com’s Thomas Harding tweets. The 24-year-old will certainly miss all of the coming season and may not quite be ready for the start of 2017, depending upon his recovery timeline.

Diaz, 24, had been expected to challenge for a role in the Colorado bullpen. He owns an upper nineties fastball that he pairs with a high-velo slider, but has struggled to keep the ball in the zone and doesn’t induce a ton of swings and misses.

Last year, he contributed 19 innings of 2.37 ERA pitching, with 8.5 K/9 against 2.8 BB/9, in his first extended stint at the major league level. Of course, Diaz sent most of his season at Triple-A and wasn’t quite as productive. There, he spun 64 2/3 frames with a 4.18 ERA while providing evidence of his control problems (8.4 K/9 against 5.4 BB/9).