The Lightning lead the best-of-7 series 3-1.
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The defenseman has an upper-body injury sustained during a 3-1 loss in Game 4 on Wednesday. He did not travel with the Devils to Tampa on Thursday but could join them later.
If Vatanen cannot play, the Devils could reinsert Mirco Mueller, who has three shots on goal and a minus-1 rating in two Stanley Cup Playoff games. They could give right-handed shot Steven Santini an opportunity to play in his first NHL playoff game.
"The situations [Vatanen] plays in, if he winds up not playing, you have to change some things around," Devils coach John Hynes said. "Sami is an important part of our team and a really good player for us, but if it's unfortunate that he isn't able to go, then it's next man up, and we've said it all along. It's not about the guys out of your lineup, it's about the performance of the guys in your lineup."