A tweet on the Stars' official Twitter account said Lehtonen suffered a lower-body injury.
Lehtonen departed during at TV timeout at 13:49 of the first period. Moments earlier, he stopped a Jordan Schroeder wrist shot with the shaft of his stick as the puck was headed for the top corner of the net.
The shot knocked Lehtonen's stick out of his hand. The save came a little while after he got his blocker on a Ryan Kesler shot before the puck hit the crossbar and bounced out.
Lehtonen stopped all seven shots he faced.
He was replaced by Richard Bachman. Lehtonen took a no-decision, and retained a 7-2-1 record on the season.