SAN FRANCISCO -- Barry Bonds tweaked his left side during last weekend's series in New York, though the San Francisco slugger initially tried to play through it.
The injury has become worse in recent days, and Bonds grimaced after a swing during Tuesday night's 2-1 win over the Florida Marlins.
He was already scheduled for a day off Wednesday for the finale of a three-game series with the Marlins, but now his status for a four-game series against his former club -- the Pittsburgh Pirates -- starting Thursday night was in question.
Bonds was examined by team doctors Robert Murray and Ken Akizuki late Tuesday, and trainer Stan Conte listed the slugger as day-to-day.
"I hope this is not a serious problem," Giants manager Felipe Alou said.
Bonds went 0-for-4 with a strikeout one night after hitting his 716th career home run to move within 40 of passing home run king Hank Aaron's 755.
"I don't know yet," Bonds said when asked about the severity of his injury. "I was hurt from the second inning [Tuesday]. I played ecause I didn't want to come out. ... I'm only concerned if somebody's putting me in a coffin."
Bonds, who turns 42 on July 24, said he didn't tell the team's training staff about his sore side until Wednesday morning when he arrived at the ballpark -- so he wasn't sure how the injury would be
"I felt the pain in New York but I didn't think about it then," Bonds said. "It just got worse and worse. ... I'm just sore, not too bad. It got worse and my back started hurting again. My back is not as tight today."
Bonds hit his 715th homer May 28 against Colorado to pass Babe Ruth and move into sole possession of second place on the career list behind Aaron.
The seven-time NL MVP was limited to 14 games in 2005 following three operations on his troublesome right knee.