Lehtonen lost his helmet as he fell back into the goal after the hard hit.
"Obviously, not good," Stars coach Lindy Ruff said after Dallas' 4-3 win. "[Haula] went in hard, [Lehtonen] hit the crossbar hard. Likelihood, it's a concussion on just a dirty play. He should be suspended.
"Fourth-liner takes out our goaltender."
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.
Information from The Associated Press was used in this report.