"It's not as bad as we thought, but he's definitely on the DL," Renteria said.
Sweeney came up limping after chasing down Allen Craig's fly ball in the Cardinals' eighth inning. Sweeney caught the ball, but couldn't make the throw home and flipped it to left fielder Ryan Kalish.
The Cubs selected the contract of outfielder Chris Coghlan from Triple-A Iowa to take Sweeney's spot. Coghlan, 28, was in camp as a non-roster invitee, and played in 24 Cactus League games before he was assigned to Iowa in the final days.
A left-handed hitter, he was batting .243 (17-for-70) with five doubles, six RBIs, six stolen bases, 13 walks and a .379 on-base percentage in 24 games with Iowa this year.
"Any time you're in Triple-A, it was humbling," said Coghlan, the 2009 National League Rookie of the Year. "It's a grind. I'm grateful for the opportunity to play every day and get back here."
A career .270 big league hitter, Coghlan was limited to 70 games with the Marlins last year because of a right calf injury, and batted .256 (50-for-195).
"He's a guy we can use off the bench, he's a guy who can start in the outfield," Renteria said of Coghlan. "He just continues to give us a little flexibility."
Coghlan's plan was to make the Cubs' Opening Day roster.
"There's no guarantees, but that's this industry," he said. "There's no guarantees no matter what. You have to prove yourself every day. I came with the expectation that I was going to make the team and be on the team. That's what I expected out of camp. It didn't work out, and I'm here now, so I'm grateful."
He got some advice from former Cubs outfielder and Hall of Famer Andre Dawson, now with the Marlins' front office, who recommended Coghlan play for the Cubs. They have yet to exchange text messages.
Coghlan was happy to see sunshine at Wrigley Field on Saturday. The Iowa team has had a lot of games postponed because of the weather.
"I'm sure you dealt with the same thing," he said. "It's just the way it is in the Midwest. You get through that first month, and the sun comes out, then you can do some damage."