Infante, who had two hits to raise his average to .349, left the game and X-rays immediately showed the fracture.
Braves manager Bobby Cox said he expects Infante to miss six to eight weeks. Infante had a similar injury in spring training last year.
Cox called the loss of Infante "huge."
"He's been on fire the whole year," Cox said. "He can play several positions and he can play them well."
Infante will be evaluated by Dr. Gary Lourie on Thursday.
Infante has shared time with Kelly Johnson at second base and has made fill-in starts at shortstop and third base as well as playing three games in the outfield.