The reigning NHL MVP sustained the injury from a hard check by St. Louis Blues forward Brayden Schenn on Tuesday night. Kucherov left the game with an upper-body injury, which Cooper confirmed was not a concussion.
"(We) thought he would be better when he got to the rink today but he wasn't," Cooper added Thursday, according to Lightning reporter Caley Chelios.
The bench boss added that Kucherov's availability for Saturday's game versus the Anaheim Ducks remains unknown.
Here's the hit that will sideline Kucherov against Chicago:
The 26-year-old Russian has recorded six goals and 12 assists in 18 contests this season. He notched 128 points last year during his MVP-winning campaign.