"Definitely not a day-to-day thing," Cooper said after the Lightning's skate Monday.
Kucherov did not participate in that practice, and the coach said the team is waiting on additional information about his status.
The winger appeared to suffer a lower-body injury in Tampa Bay's 2-1 overtime victory over the Washington Capitals on Saturday night. He left the ice at 9:08 of the third period, was checked by the team's trainer at the bench and then left for treatment. Kucherov skated 17:26 in the game. On the season, he has a goal and three assists in three games.
"He'll be evaluated when we get back. He's a tough kid, so hopefully this isn't too bad. But it's way too early to tell what's wrong," Cooper said after the game.
Lightning captain Steven Stamkos was a little more dramatic: "Kuch is a pretty tough guy. It didn't look good. He's one of the best players in the league. We're praying he's OK."
Neither the Lightning nor Kucherov's agent would comment on the nature of the injury. The team said it has yet to be determined whether more information would be released about Kucherov on Monday. Tampa Bay hosts the rival Florida Panthers on Tuesday night.
Kucherov is the Lightning's top right wing. His spot on their first line with center Brayden Point and winger Ondrej Palat was filled by veteran Corey Perry at practice on Monday. Palat moved up to take Kucherov's place on the Lightning's top power-play unit.