Lehtonen lost his helmet as he fell back into the goal after the hard hit.
"Obviously not good," Star coach Lindy Ruff said after Dallas' 4-3 win. "Likelihood, it's a concussion."
In Lehtonen's place, Tim Thomas made his Stars debut and stopped all six shots he faced. They acquired him from the Florida Panthers in a trade at Wednesday's deadline. Minnesota was leading 3-2 at the time.
Haula received 15 minutes in penalties, a major for charging plus a game misconduct.
I'm just excited about the opportunity. I've been on the ice earlier than usual and in the weight room, pushing around a little more weights than usual. Every day I go into a workout with a smile on my face and ready to go. When you do have a little more responsibility, you want to take your lunch pail and get ready to work.
— Brian Elliott to Jeremy Rutherford of the Post-Dispatch on being the Blues' No. 1 goalie