"I think it's pretty bad," said Mattingly. "He hasn't had an MRI, but he felt something pop. Nothing's definitive, but I don't know if there's a chance for him to play again this year. It doesn't sound very good."
Kennedy started ahead of Luis Cruz at third base because of his .381 career average against Tim Lincecum, and he homered in the top of the sixth inning to give the Dodgers a 2-1 lead.
But Kennedy was injured in the bottom half of the inning on Hunter Pence's tricky-hop single that tied the game when Kennedy was unable to get his body in position to make a play. Kennedy was on the disabled list from July 25 to Aug. 10 with the same injury.
Mattingly said right-handed hitter Juan Uribe and switch-hitter Nick Punto become the backups at third base and second base. He said the club also has considered calling up infielder Elian Herrera from Triple-A Albuquerque, which is in the playoffs.