Mulder said his shoulder didn't really hurt after the final pitch to Rollins, but "I couldn't get my arm up where it needed to be."
"It's almost like it keeps teasing me," said Mulder, meaning he has felt good and then something like what happened on Wednesday would occur.
"You keep letting people down, including yourself."
Manager Tony La Russa didn't want to rush to medical judgment just yet.
"He said he just couldn't get his arm back to where it belonged," La Russa said. "I don't know what that means, but it's certainly not good news."
The Cardinals had planned to give Mulder at least a couple of starts with Adam Wainwright on the shelf with a strained right middle finger, but Mulder almost surely will have to go back onto the disabled list.
"It's more of a tough break for him than anyone else," La Russa said. "I feel really bad for him more than for us."
With Mulder going out so early, the Cardinals had to overwork their bullpen again. Right-hander Brad Thompson, who got out of the first when he retired first baseman Ryan Howard on a double-play ball, pitched sturdily into the fifth before allowing two runs.
After the Cardinals caught up, Kyle McClellan (1-4) gave up a home run to Howard on an 0-2 pitch in the eighth.
"He needed to bounce it," La Russa said.
PHILLIES 4, CARDINALS 2: Rookie RHPs Kyle McClellan and Chris Perez each served up a home run on a bad breaking ball in the eighth inning as a 2-2 tie became a loss. The Cardinals had their best chance in the seventh when, after they tied the score, rookie Joe Mather was sent up to pinch-hit against RHP Chad Durbin with the bases loaded. Mather struck out.
NOTES & QUOTES
--General manager John Mozeliak said, "We don't want to position ourselves where there's a knee-jerk reaction" to the big-name pitching acquisitions made by Chicago and Milwaukee, the Cardinals' two competitors in the National League Central Division.
Mozeliak said the club still would be searching for left-handed relief help immediately but would want to buy a little time to see how RHPs Adam Wainwright and Chris Carpenter respond. Wainwright (sprained right middle finger) and Carpenter (elbow surgery) are throwing. Both could be ready by early August.
--LHP Randy Flores, on a minor league rehabilitation assignment as he recovers from tendinitis in his left ankle, worked a scoreless inning Tuesday for Class AAA Memphis in his first appearance.
--3B Troy Glaus, after lining out twice with runners on base to end innings, blooped a run-scoring single in the seventh to end an 0-for-21 slide.
--Backup C Jason LaRue had a strong game with a single and a double, and he threw out a runner trying to steal.