Ahead of their pivotal series against the Cubs, the Giants placed lefty reliever Jeremy Affeldt on the DL with a left knee subluxation retroactive to Monday, August 24.
RHP Mike Broadway was recalled from Triple-A Sacramento to take Affeldt's spot in the bullpen.
Giants manager Bruce Bochy explained to reporters before Tuesday's game that Affeldt injured his left patella.
Asked how the 36-year-old suffered the injury, Bochy said it happened on Monday when the Giants were off.
"Just spending a day with his kids running around. Just Jeremy being Jeremy," Bochy said. "He said he wasn't doing anything crazy, just running around and he hurt himself."
In 31.1 innings pitched over 44 appearances this season, Affeldt has a 5.46 ERA and 20 strikeouts.
The 28-year-old Broadway made his major league debut with the Giants on June 13. He got into six games and allowed three earned runs in 7.1 innings pitched.