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've got a lot of experience and there's a lot of young guys. It's even making me excited a little more. It's kind of a new life. At my age, I feel like I know a lot of things what to do, but I just cannot do it anymore. It's a lot easier to tell them what to do because they've still got the legs and hands to do it. I just know things, but I cannot do them anymore.
— Jaromir Jagr after making his Panthers debut in a win against the Sabres on Saturday