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.
It's not just going to happen on its own. We have to have guys commit to the areas we need to improve on. We're going to be better than last year but there is still a long way to go. But I really like the pieces and where we're headed.
— Sabres forward Tyler Ennis on the progress of Buffalo's rebuilding process