Tim Thomas started the Stars' past three games, with Nilstorp serving as his backup. The Stars are 1-1-1 without Lehtonen.
Nilstorp played in one game, replacing Thomas 29 seconds into the second period of the Stars' 7-2 loss to the Winnipeg Jets on Sunday. He allowed three goals on 17 shots in his two periods of action.
Lehtonen is 25-16-10 with a 2.47 goals-against average and .917 save percentage in 53 games, but had won four of his five starts prior to his injury.
The Stars next play Tuesday at the Pittsburgh Penguins.