"It's not as tight as it was," Zambrano said. "Just going to take it one day at a time. Nothing to worry about."
Zambrano, who has had back trouble before, said he began the game in discomfort and then aggravated the problem. He left after allowing seven runs in 2 1/3 innings and took the loss, which left him 4-4 with an ERA of 3.55.
The Marlins have two off days in the next eight days, allowing them flexibility if they decide Zambrano is not ready to take his next scheduled turn.