Lehtonen was injured in a 4-3 win over Minnesota on March 8 when Erik Haula ran him over and knocked off his helmet. He went through his first full practice Friday.
Tim Thomas made four starts in Lehtonen's place, including a game against Columbus that was postponed when Stars forward Rich Peverley collapsed on the bench in the first period. Thomas was acquired from Florida a day before the trading deadline.
Thomas was pulled from Sunday's 7-2 loss at Winnipeg after allowing his fourth goal on 17 shots just 29 seconds into the second period. Nilstorp finished the game.