In the first period of the tilt, Kucherov took a hard crosscheck to the body from Islanders defender Scott Mayfield. Soon after, the Lightning winger tried to hit Mathew Barzal but appeared to injure his arm. He left down the tunnel moments later, just 2:22 minutes into the game.
Kucherov, who currently leads the Lightning — and all playoff skaters — in scoring, did not return for the second period.
Head coach Jon Cooper did not have an update on Kucherov's status after Game 6 or when he met with media Thursday morning.
"No update," Cooper said Thursday morning. "This isn't new for us, you just move on, and if you're fortunate enough to win the game it makes for one hell of a story."
Tampa Bay also briefly lost forward Ross Colton to the locker room, taking them down to 10 forwards, but the rookie returned later in the second period.
Currently up 3-2 in the series, the Lightning are looking to seal the semifinal win and book their place in the Stanley Cup Final for the second straight year.