St. Louis was taken to a hospital for examination.
"I assume he won't be able to play tonight," Lightning GM Steve Yzerman said. "I don't know specifically if it was on the eye, but it was in the area of the eye. I don’t know if it hit him in the orbital or the cheekbones. It's a difficult loss for the team, but you know what? It's an opportunity for guys to step up."
St. Louis was circling behind the net when teammate Dominic Moore missed the net with a backhander and caught St. Louis near the eye. The Lightning's second-leading scorer skated to the bench and was immediately helped to the locker room by a trainer.
If he misses the game, it will end the 36-year-old's 499 consecutive games played streak, which is the second-longest active streak in the NHL behind Calgary's Jay Bouwmeester, who has played in 531 straight.
For more on St. Louis and the Lightning, visit Raw Charge.