ST. LOUIS -- St. Louis Cardinals first baseman Lance Berkman could miss the weekend series against the Chicago Cubs with a left calf strain.

An MRI showed no significant problem for Berkman, who said Thursday the calf was much improved from a day earlier when it was very sore. He considered himself day to day.

Berkman was injured legging out a triple at Cincinnati on Tuesday.

"It was real sore yesterday as you might expect the day after but today it feels better and the MRI was good," Berkman said. "They basically said you're not going to necessarily damage it any worse, just be smart."

Manager Mike Matheny said Matt Carpenter and Daniel Descalso could fill in at first base while Berkman is out. The Cardinals play their home opener on Friday against the rival Cubs.

Berkman was hitting .375 with one home run, six RBIs and a .565 on-base percentage.

"We have good news with the MRI; we know it's just kind of day to day with him," Matheny said. "I know he'll be pushing the envelope and we'll follow the medical staff."

Berkman said the calf got tighter as he rounded the bases, but that he didn't really notice until he slid into third base. He left the game after singling in his next at-bat.