On Friday, Oakland Athletics breakout starter Frankie Montas was suspended 80 games after failing a performance-enhancing drug test. The A’s suffered another loss to their pitching staff on Sunday, as they placed closer Blake Treinen on the injured list due to a strained shoulder. It’s unclear how long Treinen will miss, though his stint is retroactive to Friday:

Treinen, who made the All-Star team and earned votes for the Cy Young and MVP Awards last fall, has not been as effective this year. He hits the shelf having compiled a 4.08 ERA (106 ERA+) and a 1.61 strikeout-to-walk ratio in 35 innings. Already he’s walked as many batters (21) as he did all of last season in 45 additional frames.

It’s worth noting Treinen’s struggles have coincided with an approach tweak. He’s thrown his sinker less often in place of his four-seamer, and has used his cutter more than his trademark slider — an offering that batters hit .141 on last season, while whiffing on more than half their swings taken against it. Treinen’s reasoning for the shift is anyone’s guess.

What isn’t a guess is who is in line to take Treinen’s spot as closer. Liam Hendriks has been Oakland’s best and most reliable arm out of the bullpen, posting a 1.49 ERA and 2.94 strikeout-to-walk ratio. The other top options — Joakim Soria and Lou Trivino — are sporting ERA above 5.00. Bob Melvin used Hendriks for the save opportunity on Saturday.

Whether or not Treinen is out for long, one name to watch heading forward is A.J. Puk. The Athletics are easing him back from Tommy John surgery as a reliever, and it’s at least possible he factors into their late-season plans — particularly if they remain competitive.

The A’s entered Sunday seven games back in the division race and a game behind Cleveland and the Boston Red Sox for the second wild card.