CHICAGO (AP) -- Cubs pitcher Carlos Zambrano left Thursday's start against San Francisco in the second inning because of soreness in his lower back.
Zambrano had just thrown a ball to Eli Whiteside after an RBI single by Miguel Tejada when he began stretching his back.
Trainer Mark O'Neal and pitching coach Mark Riggins rushed out and manager Mike Quade followed. Marcos Mateo then relieved with the Giants leading Chicago 1-0.
Zambrano has struggled at times this season but had been pitching well of late, going at least seven innings in his previous two starts against the White Sox and Kansas City.