O’Brien will replace the recently demoted Ryan Fernandez in the Cardinals’ bullpen. The 30-year-old right-hander has made seven appearances at Triple-A Memphis this season, posting a 3.86 ERA, 1.14 WHIP and a 14/3 K/BB ratio over seven innings. Expect him to be used in a middle relief role by the Cardinals.

O’Brien missed four months last season due to a flexor tendon strain and dealt with some recurring pain earlier this spring. The 30-year-old righty made a Grapefruit League appearance on Friday evening for the first time in nearly three weeks and will open the year back in the minors as extra organizational relief depth.

O’Brien hit the injured list back at the end of spring training with a right flexor strain and is finally ready to make it back to the big leagues. The 29-year-old righty has looked dominant this season at the Triple-A level, posting a sparkling 1.35 ERA, 0.98 WHIP and 9/5 K/BB ratio across 13 1/3 innings (14 appearances), so the Cardinals probably want to see what he can do at the highest level.