De La Rosa, who had thrown three perfect innings to that point in arguably the biggest start of his career in a pitchers' duel against Clayton Kershaw, came out after throwing a 93 mph fastball to Rafael Furcal in the fourth inning on his 40th pitch of the night.
De La Rosa said after the game that he hopes to be fine to start in the National League Division Series against the Phillies even if his start is pushed back to Saturday or Sunday in Game 3 or 4 at Coors Field.
"I'm worried a little bit, but I think I'll be OK," said De La Rosa, who suffered a similar injury in the last start of the season last year as well and said it took about a week for the pain to subside. "We'll see tomorrow how I feel."
Rockies manager Jim Tracy said it's too early to speculate on De La Rosa's status until he is checked out by team doctors on Sunday.
"I think the important thing is that we have to allow it to run its course tonight, and tomorrow we'll have a chance to reassess it," Tracy said. "You never want to make a decision after it occurs. We want to wait for our medical staff to take a look at him tomorrow before I say something that could be totally wrong."
It's a scary situation for the Rockies as De La Rosa has been one of the best left-handers in the league as evidenced by the fact that his 16 wins lead all National League lefties. He's also been dominant in the second half of the season with a 12-2 record and a 3.43 ERA since July 1.
He leads the Majors with 16 wins since June 1 after going 0-6 in his first 10 starts of the season.
De La Rosa was replaced by Jose Contreras, who gave up a single to Furcal just two pitches later. But Contreras got out the jam by getting Juan Pierre and Matt Kemp to ground out before Manny Ramirez lined out to right to end the inning.
The injury ended a great night for De La Rosa, whose excellent outing before his exit was similar to the one he made two weeks ago in a crucial game against the Giants in which he threw eight scoreless innings in a Rockies win.
"His start resembled an awful lot like the game he pitched against the Giants," Tracy said. "But unfortunately he told us that his left groin was tight and we weren't going to take any chances with it. He wanted to try to throw a couple pitches, but that was out of the question also."
Rhett Bollinger is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.