ST. LOUIS -- A series of exams on Jason Heyward's tight hamstring Tuesday revealed the Cardinals outfielder is dealing largely with a cramping issue. That is, as manager Mike Matheny described, "good news" for a team that already has three outfielders on its disabled list. Heyward, though out of the lineup Tuesday, will not be joining them.

"We're going to continue to go slow, but it is a good report from what we're getting," Matheny said before the Cardinals' 2-0 loss to the Giants on Tuesday. "Now it's just going to be on how he feels and doctors testing strength. That's something that could be extremely quick."

Heyward exited Monday's game with left hamstring tightness after two innings. He had struck out in his only at-bat and done minimal running in the field, but Matheny noted the cramping could have been related to the extensive pregame work Heyward did to prepare for his first start in center field. Heyward agreed.

"I ran around in [batting practice] more than I have been, more than I would normally this late in the season, just to try to get acclimated to center field, not having played it that much," Heyward said after sitting out Tuesday's game. "I was just trying to do my due diligence for myself and for my teammates, knowing that I'm going to go out there and play a good center field.

"I didn't think I had popped anything. But at the same time I did feel tight before the game. I tried to get it loose. I wasn't going to pull out. I knew we were already short a guy. I was hoping it would loosen up, but it never did. It was actually kind of hard to accelerate. It was the right move to take me out of the game, and it was a smart move not to play today."

Video: [email protected]: Heyward strikes out, later exits game

Though Heyward wasn't sure the cramping was related to dehydration -- an issue that forced him out of a July 18 game prematurely -- he did receive IVs on Tuesday. He went through a series of tests around game time to determine his status but was not cleared to play, which left Matheny with a three-man bench.

While the Cardinals haven't ruled out Heyward's availability for Wednesday's series finale against the Giants, Heyward acknowledged the greater likelihood is he'll sit out one more game, rest on Thursday's off-day and then return to the field in San Diego during the team's upcoming weekend series.