ATLANTA -- Brendan Ryan sustained a left hamstring injury in the fifth inning of the Cardinals' game against the Braves on Wednesday night and is likely out at least five-to-seven days. Ryan could also miss 15 days, since the Cardinals probably will be forced to make a roster move before Thursday night's game against the Nationals in Washington.

Batting with no outs in the top of the fifth inning, Ryan hit a bouncer to the left side of the infield. As he legged out the ball, he slowed shortly before reaching first base and reached for a spot high on the back of his left leg. The ball was called foul, making Ryan's effort moot and adding to the frustration of the injury.

Head athletic trainer Barry Weinberg came to check on Ryan, and a decision was made promptly not to allow him to continue playing. Brian Barden replaced Ryan.

"I've pulled it before, and I've done it a lot worse," Ryan said. "It's a new one to me, because any time I've ever had a tweak or a pull or anything, it was getting going. It was exploding, working up to full speed. So it was strange that it happened where it did."

The timing could scarcely have been worse, for Ryan as well as the team. Regular shortstop Khalil Greene is sidelined with a right forearm injury, which is why Ryan was starting in the first place. Additionally, Ryan had been playing some of the best baseball of his career, on offense as well as on defense. In the bottom of the fourth, he made a highlight play on a Javier Vazquez grounder.

"I had a good shot to see some innings here, and that makes it all the more frustrating," Ryan said.

With Greene unavailable to start, even if Ryan is out for only a short time, a roster move is likely imminent. Among the candidates for promotion are third baseman David Freese and infielder Tyler Greene, both of whom are at Triple-A Memphis. The Cardinals remain reluctant to cut back to 12 pitchers, so one viable course of action would be to place Ryan on the 15-day disabled list.

"He's playing great, and right now we've got a need for a shortstop, so this was going to be a good opportunity for him," manager Tony La Russa said. "I was just talking to the trainer. He's going to be out for a few days. I'm going to talk to [general manager John Mozeliak] here in a little bit, but I don't know how much shorter we can play. So my guess is we'll have to do something."