"We'll have a better idea tomorrow how sore he is and the severity of it," Reds manager Dusty Baker said.
For a roster that's been ransacked by injuries all season -- eight players currently reside on the disabled list, including two members of the rotation -- Cueto is the latest to have some kind of physical setback.
"Since the first inning, it was bothering me," Cueto said with teammate Carlos Fisher translating. "It got a little tight to start the day, but it didn't really bother me until the first inning."
Cueto was the leadoff batter in the top of the third inning during a 1-1 game and clearly looked pained as he grounded out to second base. He barely ran down the line even though Cardinals pitcher Kyle Lohse had to cover first base on the play to complete the out.
Baker made the decision to get Kip Wells up in the bullpen and pulled Cueto even though he wanted to continue.
"He said he was cramping," Baker said. "I could tell something was wrong when he didn't run to first base. He was tight early in the game. When I looked up, he didn't have his normal velocity. He wanted to go back out, but we couldn't take a chance of hurting him."
The 23-year-old Cueto didn't believe the injury would force him to miss his next scheduled start on Saturday vs. the Nationals.
"I think I will be alright," Cueto said. "I didn't want to risk anything. It shouldn't be a problem."
Currently, the Reds' rotation is without Edinson Volquez, who is out for the season and perhaps all of 2010 after he had Tommy John ligament replacement surgery on his right elbow. Micah Owings is on the DL with shoulder tightness but made a rehab start on Monday at Triple-A Louisville.
Jay Bruce (broken wrist) and Ramon Hernandez (knee surgery) are among position players that the Reds are still missing. Six different players have required surgery this season.
Add it up, and it plays a large role in the Reds' sharp second-half decline. At 48-63, fifth-place Cincinnati is 13 1/2 games behind first-place St. Louis in the National League Central.
"In 2006 with the Cubs, we lost a lot of guys -- key guys too," Baker said. "I've always said the team that keeps their front-line players out there the most is the team that wins. That's why they're front-line and that's why they're key."
Signed on July 7 for depth protection at Triple-A Louisville after being released by the Nationals, the well-traveled Wells found himself making his Reds debut under tough circumstances. Pitching for the first time since his July 31 callup, the right-hander retired his first seven batters after taking over.
Then came trouble. Yadier Molina hit a one-out single to right field before eighth batter Brendan Ryan walked. Lohse sacrificed the runners over, and Skip Schumaker walked on four pitches to load the bases.
It took five pitches for Rasmus to earn the free pass from Wells (0-3) that got Molina home.
"I just got tired and lost the ability to regroup as far as not being in a game for 10-12 days," Wells said. "There have been times in my career where I've walked too many guys. In this case, I wasn't trying to be too fine or miss the bat. I was trying to throw the ball over the plate."
Wells was lifted for Jared Burton, who drew the task of facing Pujols with the bases loaded. In the clubs' previous series in Cincinnati, he smoked a grand slam. This time, Pujols -- a .363 lifetime hitter vs. the Reds with 38 homers and 114 RBIs -- hit a routine fly to end the inning.
Lohse (5-7) pitched six innings and allowed one earned run and four hits with three strikeouts. The Reds' lone run came in the top of the first when Willy Taveras doubled and scored on Brandon Phillips' sacrifice fly.
More pain and suffering came in the sixth inning after a Matt Holliday drive to center field off Burton. Taveras ran at full speed and crashed headlong into the wall, barely missing the catch. He spent several moments on his back and needed to be looked at by the trainer and Baker but remained in the game.
A few moments later, Khalil Greene sent Taveras to the fence a second time with a drive to left-center field. This time, Taveras was more tentative as the ball bounced off the wall for an RBI double. Ryan drove in Greene with his own RBI double to left field, icing St. Louis' win.