For Modano, the move announced Tuesday is retroactive to Oct. 3, when he injured his ribs in the season opener against Nashville.
Lehtinen injured his groin Oct. 14 against the Predators. He has one assist in four games this season.
The Stars recalled winger Francis Wathier from the Texas Stars of the AHL and reassigned center Perttu Lindgren to their primary affiliate.
Lindgren made his NHL debut in Monday night's 4-1 loss to the Los Angeles Kings.