They expect him back Thursday night when they host the Calgary Flames, who have several players that have had success against Dallas recently.
The Stars (3-5-0) have been without Lehtonen since a 4-1 win at Winnipeg on Oct. 11, which he left due to a lower-body injury. He is 2-1-0 with a 1.57 goals-against average in three games.
With Lehtonen sidelined, Dallas has lost four of five while allowing five or more goals three times. Dan Ellis and rookie Jack Campbell haven't proved reliable in his place, combining for a 4.40 goals-against average since the injury, the worst in the league during that span.
Campbell started a 6-3 loss at Anaheim on Sunday in which the Stars squandered a 3-1 lead after the first period.
Lehtonen was activated from injured reserve Monday and is expected to play after being a full participant in Tuesday's practice. He's had mixed results against Calgary, going 6-3-2 with a 2.85 goals-against average.
"It takes a little time to be a good goalie again, and we are on the right track," he told the team's official website. "Being a goalie is not painful anymore. I am able to make saves. A week ago, I wasn't able to do much.
"Every day we've been able to do more and more, and we are almost there."
Calgary (4-3-2) has lost three of four on a five-game trip, falling 4-2 to Phoenix on Tuesday. The Flames tied the game in the third period after trailing 2-0 midway through the second.
"The second period, we got going," coach Bob Hartley said. "I really liked our last 40 minutes. We gave ourselves a chance to win the game."
Lee Stempniak and Jiri Hudler continued their strong starts, with Stempniak scoring his third goal for his eighth point. Hudler was credited with an assist to extend his point streak to nine games, during which he's totaled 12 points.
Hudler has six goals in his last six matchups with Dallas, while Stempniak has recorded at least one assist in each of his past four.
Calgary's Michael Cammalleri, who returned from a hand injury to play the last two games, has eight goals and seven assists in his past nine games against the Stars.
The Flames have also received some of the worst goaltending in the league with a 3.44 GAA.
Calgary is the worst penalty killing team in the NHL, having allowing nine goals in 29 opportunities (31.0 percent) and five on 15 chances over the last three games. Dallas hasn't been much better, surrendering seven goals on 32 power plays (21.9 percent).
The Flames have won three of the last four meetings, going 8 for 17 on the power play.