Richards, who played in New York's 20 games this season before Tuesday night, returned to the ice Sunday after being shaken up in the third period of the Rangers' 3-2 shootout victory over Buffalo. He remained down for several minutes and received treatment before feeling well enough to finish the game.
Richards also skated briefly on Tuesday morning, but was ruled out about 90 minutes before the Rangers were to face the Flyers.
Rangers coach John Tortorella said Richards was "banged-up" but didn't give specifics about his injury. Tortorella also said he doesn't believe this will be a long-term problem.