The Rockies have designated right-hander Jairo Diaz for assignment and selected the contract of left-hander Jerry Vasto from Triple-A, according to a team announcement. Additionally, Colorado has placed reliever Scott Oberg on the disabled list with a back strain.
The hard-throwing Diaz joined the Rockies prior to 2015 and saw action with the team that season and during the 2017 campaign, combining for a 3.75 ERA with 7.5 K/9, 4.13 BB/9 and a strong 57.3 percent groundball rate over 24 innings. But Diaz underwent Tommy John surgery in 2016, causing him to miss that season, and has only tossed 28 2/3 innings between the majors and minors since. Diaz opened 2018 with 3 2/3 frames of four-earned run ball at the Triple-A level, and he has been shelved with forearm tightness since mid-April, Nick Groke of the Denver Post tweets.
Vasto, 26, is set to make his MLB debut after initially joining Colorado as a 24th-round pick in 2014. He ascended to the Triple-A level last season and has been particularly effective this year, having logged a 1.71 ERA with 11.14 K/9, 3.43 BB/9 and a 47.9 percent grounder rate in 21 innings.