ST. LOUIS -- The Cardinals placed right-handed reliever Jason Motte on the 15-day disabled list on Wednesday due to a shoulder injury and recalled right-hander Fernando Salas from Triple-A Memphis to take his roster spot.

In a release, the Cardinals referred to the injury as an "AC sprain" in Motte's right shoulder, while Motte called it a "grade 1 AC shoulder separation." The move is retroactive to Tuesday. Manager Tony La Russa said he hopes that Motte will be available as soon as the requisite 15 days are over.

Motte, 28, felt something amiss on Monday night and underwent an MRI exam on Tuesday. However, he expressed little concern about the condition on Tuesday when he spoke with reporters. He has been dealing with sporadic shoulder discomfort since April, he said.

"It's been off and on all year," Motte said. "So I've been feeling it and not feeling it. Going out there and kind of pitching with it. So, it's one of those things where the other day I didn't even feel it when I was out there, but I went back and watched the video and I was throwing way down here. I had no idea where the ball was going."

In the Cardinals' Monday night game against the Astros, Motte reported discomfort in his shoulder to the Cardinals' training staff but not the coaching staff. He received heat on the joint after pitching the seventh inning, then came out to pitch the eighth.

In the eighth, though, he was not the same pitcher. He issued walks to the first two batters, throwing balls on his last five pitches.

"The thing was, it's the value of experience, he felt like he was dropping his arm when he warmed up," La Russa said. "That's a painful lesson for him and for us. But there wasn't any bad intention there because he's pitched with some soreness before. They say it doesn't affect his pitching."

Motte has been an integral part of the Cardinals' bullpen this season. He's 3-2 with a 2.70 ERA, two saves, 42 strikeouts and 16 walks in 43 1/3 innings. He has the most appearances of any right-hander on the staff.

Salas, 25, will be with the Major League club for the fifth time this season. In 10 appearances covering 11 2/3 innings, he has a 2.31 ERA, nine strikeouts and four walks.