"It's been a gradual thing," Richards said. "I noticed it in the exhibition games. But I rested, and it went away.
"It's very frustrating. But I'd rather have it now than close to playoff time."
Richards also fought through nagging groin pain in captaining Canada to the world junior championship in North Dakota earlier this month. That's the kind of competitor he is.
The Rangers have scheduled tests to determine if Richards has underlying problems. Trainer Dan Lebold says the team is taking no chances on Richards pushing himself too fast and possibly tearing muscles.