"It's been feeling sore, and I decided to have the doctors check it out," Beltran said after Thursday's loss to the Marlins.
Beltran, who has not played since the Mets clinched the National League East title on Monday, has talked with manager Willie Randolph and the two have agreed that the MVP candidate will be day-to-day until the playoffs.
On Thursday, Beltran took batting practice and ran "about 10 wind sprints" in addition to his usual stretching routine. He said his leg felt better than it has the past few days, and mentioned that it has been getting better each day since Sunday.
The All-Star outfielder believed the injury happened when he made a running catch in the game against the Pirates. He knew there was something wrong, but he didn't consider it to be that big of a deal. He felt sore on Monday, but he thought it was wear and tear near the end of a long season.
Beltran received treatment before Monday's game and played in the clincher. He felt tightness again during the game when he scored from second on a single by David Wright.
"I don't have any problem hitting, and I still have been taking at-bats in the cage," said Beltran. "The problem is when I play defense and I'm running the bases. I just have to wait and see."
When asked if it would be a situation that might hold him out of the playoffs, though, Beltran was adamant that he would still play.
"I will play," declared Beltran. "I won't miss that. Obviously, it's good that we clinched so that I have some days to recuperate.
"The doctors said if I feel good, go out and play. If I can't run in the field and on the bases, though, they said not to. But I will still play in the playoffs."
Beltran, who is batting .277, leads the team with 114 RBIs, 121 runs and 40 home runs.
Chris Girandola is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.