OAKLAND -- It was a rare sight to see someone other than Blake Treinen on the mound for the A’s with a two-run lead in the ninth inning on Saturday, but that will become a more common occurrence for at least the next 10 days.

Treinen was placed on the injured list (retroactive to Friday) with a right shoulder strain on Sunday morning. Right-hander Brian Schlitter was called from Triple-A Las Vegas in a corresponding move.

Treinen underwent an MRI before Saturday’s 4-2 win against the Rays, and results revealed a mild strain of his rotator cuff. The issue is something the 30-year-old right-hander said he has been dealing with for a couple of weeks now.

“Anybody that pitches has tenderness to throw through,” Treinen said. “There’s days I feel pretty good, and days when it’s restricting. Today is the day we just decided to step back and let it heal.”

Coming off an All-Star campaign in which he compiled an 0.78 ERA and saved 38 games in 68 appearances, Treinen’s effectiveness has dipped. He owns a 4.08 ERA and has converted 16 of 18 save opportunities through 30 games this season.

Treinen denied there was any connection between his shoulder issue and his recent performance. He has allowed nine earned runs across his past 11 appearances (7.36 ERA), dating back to May 25.

Liam Hendriks got the call in place of Treinen and struck out two batters in a perfect ninth to record his second career save. He is expected to continue that role with Treinen out.

It’s an easy call for A’s manager Bob Melvin, with Hendriks enjoying an uptick in his fastball to around 98-99 mph and allowing just one run in his past 11 2/3 innings, with 16 strikeouts and four walks.

“He’s moved all the way up from a guy that was pitching behind in games for the most part, and now he’s got himself in the closer’s role,” Melvin said. “It’s not easy to close a game when you haven’t done it often, and against a pretty good lineup. That was impressive.”

The roles have differed throughout the year, from opener to multiple-inning middle relief, but the results have been consistent. Hendriks carries a 1.49 ERA over 35 games and is ready to pitch in whatever role the A’s need.

“I’m throwing the ball well right now, so I’m happy to be doing that,” Hendriks said. “If it’s in the ninth, it’s in the ninth. Doesn’t change my mentality. I’m one of those guys that needs to be balls-to-the-wall no matter what situation it is.”