Headley flied out to center in the top of the second Thursday night, then did not take his spot in the field in the bottom half.
Alexi Amarista replaced Headley at third base and in the fifth spot in the batting order.
He was slowed by a strained right calf during spring training and missed the first 14 games last season because of a fractured left thumb.
Headley could land on the disabled list as early as Friday.
"My guess is it's not as severe as that was," Headley said, according to MLB.com. "I expect it to be two or three weeks. I guess the silver lining is it will help the rest of my body heal."
Headley, who led the NL with 115 RBIs in 2012, entered the game batting .188 with two homers, seven RBIs and more strikeouts (20) than hits (13).
Information from The Associated Press was used in this report.