Zambrano was to undergo an MRI, and Cubs manager Lou Piniella said he expected to have a more definitive report on the right-hander on Monday. His next start is scheduled for Friday, when the Cubs open a weekend series against the Milwaukee Brewers.
"I would say right now that's in jeopardy, and if I had to guess, I'd say no," Piniella said of Zambrano making his next start.
The Cubs most likely would call up a starter from their Minor League team, if necessary. The team has avoided using the disabled list this season, despite injuries to key personnel like Aramis Ramirez and Milton Bradley.
Zambrano bunted toward third base to lead off the fifth. He sprinted down the line and appeared to extend his left leg to make sure he hit the bag. He came up limping, and athletic trainer Mark O'Neal went to first to talk to the pitcher, who apparently convinced O'Neal that he should stay in the game.
O'Neal then spoke to Piniella, who had come part of the way out of the dugout. Piniella went back into the dugout, then came out onto the field and headed over to first to talk to Zambrano.
The pitcher remained in the game, but only temporarily. Piniella came back onto the field and lifted Zambrano for a pinch-runner, pitcher Rich Harden. Zambrano then slowly walked back to the dugout. The problem is in the "belly" of the hamstring, Piniella said.
"I tried to initially [take Zambrano out], but he told me that it was more of a cramp than anything else," Piniella said. "After a pitch, he realized it was more than that. I tried to get him out initially, and he talked me out of it. We did the right thing getting him out."
Zambrano, who had given up two runs on four hits and one walk over five innings before he was pulled, ended up with the win, thanks to Derrek Lee's grand slam that inning. The Cubs beat the Marlins, 6-4.
"[Zambrano] laid down a perfect bunt, and he was motoring to first," Piniella said. "That's one of the reasons we scored four runs that inning."
On Saturday, Piniella defended using Zambrano as a pinch-hitter, which he did in both Friday's and Saturday's games, because the team is shorthanded.
"What are we supposed to do?" Piniella said on Sunday. "He laid down a perfect bunt. He hurts his hamstring, but what can you do? I thought it was a really good play. The third baseman was giving him a base hit, and he dropped it down."
Zambrano, a two-time Silver Slugger winner, does like to hit.
"This guy, there's nothing he can't do," Lee said of the Cubs' Opening Day starter, now 3-1. "He's just a tremendous athlete, [a] good hitter. He lays down a perfect bunt and was flying down the baseline. You don't see too many guys his size as athletic as he is."
The game was briefly delayed as both teams waited for a pinch-runner to emerge. Harden finally ran onto the field. Apparently, he had to find his shoes.
"I told [pitching coach] Larry Rothschild that, in the position we're in, one of our pitchers needs to keep spikes on," Piniella said. "We'll make sure a pitcher has spikes on before a game starts. I was looking for Harden, and we couldn't find him. He was back getting his shoes on. We'll keep an extra pair of spikes in the dugout."
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.