St. Louis Cardinals ace Adam Wainwright is expected to miss the rest of the 2015 season due to an Achilles injury he suffered Saturday night while stumbling out of the batter's box.

The Cardinals placed Wainwright on the 15-day disabled list Sunday with what they termed as a left ankle and Achilles injury. He is scheduled to undergo an MRI on Monday.

He tried to hide the stress of the situation after the Cardinals' 6-3 loss at Milwaukee on Sunday.

"There's nothing I can do about it, so might as well not be nervous about it or worried about it," Wainwright said. "Worry doesn't do anybody any good."

General manager John Mozeliak told KMOX Sports on Sunday that "I would imagine that with this injury he will not pitch again this season."

After Saturday's 5-3 win over the Milwaukee Brewers, Wainwright was wearing a protective boot on his left ankle. He said it felt like something had hit him in the back of the ankle.

"It felt like I got hit by something," Wainwright said. "If you look at the replay, I kind of get out of the box and look back to think, gosh, the catcher's mask must have hit me or the bat must have hit me or something must have hit me. Crazy game, something crazy like that you can never think.

"What was that, top of the fifth inning? It's going to take a lot to get me out of the game."

Cardinals manager Mike Matheny said any length of time without Wainwright would be tough.

"I think the test is going to be, with Adam, and everyone in here can see the difference in our attitude," Matheny said. "We treasure every win we have, but it was different in here last night. We're just going to hopefully let the guys go back out there and play. They had a little time to think about some of this and the response and the answer is, we knew that some tests were going to come. And this is a big one that we're getting early. Let's see what we're made of."

Wainwright had a 2-0 lead Saturday when he stumbled getting out of the batter's box on his popup that led off the fifth inning. He was helped off the field by a trainer and left the game.

"It's something in the back of my ankle, so we'll see what it is on Monday," Wainwright said Saturday night. "Everything right now is just all speculation."

Wainwright one of MLB's best since 2012 Adam Wainwright missed the 2011 season after undergoing Tommy John surgery, but since his return in 2012, he has been one of the best pitchers in the majors. Wainwright, since 2012 MLB Rank* Shutouts 7 1st CG 13 1st Wins 55 2nd HR per 9 IP 0.52 2nd ERA 2.99 6th *Among pitchers with minimum 50 starts

-- ESPN Stats & Information

The batting injury is likely to ramp up the long AL vs. NL debate on the designated hitter, as in whether it's worth having pitchers bat. Max Scherzer, who injured his thumb batting last week, said it's time for the NL to add the designated hitter.

The Cardinals recalled catcher Cody Stanley from Triple-A to take Wainwright's place on the 25-man active roster.

Starting catcher Yadier Molina, who was forced out of Friday's 3-0 win over the Brewers after being struck on the right knee guard by a foul tip, also sat out Sunday, when Tony Cruz started in his place. The Cardinals are hoping Molina won't miss much more time.

Matheny said the Cardinals have not determined who would start in place of Wainwright on Thursday against Philadelphia.

"I'll just cover the whole thing and say we're looking at everybody and try to think long term, try to think short term and have a long list of guys that we think could come in here and help us out," Matheny said Sunday. "Just trying to put it together right now, but not ruling out anybody."

Lance Lynn, the losing pitcher Sunday, said there was no extra pressure to step up and fill Wainwright's shoes.

"No," Lynn said, "we've just got to be ourselves."

Wainwright's setback comes just as he was settling into top form.

"It was by far the best I felt this year," Wainwright said Saturday night. "I really had things working. I started changing arm angles a little bit, working in and out better than I have been and I just was having a lot of fun out there. It reminded me of last year a lot.

"Those strides I was talking about making over the course of the year, I started to make them today. That's the hardest part just knowing I was making such good adjustments, and now I've got a setback."

The Associated Press contributed to this report.