Lehtonen was injured in the third period Saturday night in a win over Minnesota when Erik Haula ran over him and knocked off Lehtonen's helmet.
Stars coach Lindy Ruff said Sunday that Lehtonen was "not doing that well" after saying after the game that his goalie likely had a concussion. The team didn't update Lehtonen's condition any further.
Tim Thomas, acquired in a trade with Florida at the deadline last week, replaced Lehtonen and got the win when the Stars scored twice in the final 10 minutes to beat the Wild 4-3. He's likely to start Monday night against Columbus, with Nilstorp backing him up.
If you want to prove people wrong, you've just got to go out and do it. Yeah, we blew 3-2 series leads the last two years, but no one is going remember that if we go out there on Saturday night and beat these guys and go play in the Stanley Cup Final. We need to get back to work and we'll start to do that tomorrow.
— Ducks forward Kyle Palmieri following a loss to the Blackhawks in Game 6 on Wednesday