The Thrashers received defenseman Ivan Vishnevskiy and a fourth-round pick in the 2010 draft. Atlanta said Vishnevskiy, 21, is expected to report to AHL Chicago.
Atlanta traded leading scorer and team captain Ilya Kovalchuk to New Jersey on Thursday for three players and a first-round pick.
Lehtonen, a native of Finland, posted a 94-83-17 record in 204 games with Atlanta, setting franchise records for wins and games played by a goaltender. He has not played in the NHL this season following two back surgeries.
Lehtonen was recalled from a conditioning stint with AHL Chicago on Feb. 7. He posted a 1-1-2 record with a 2.67 goals-against average in four games with Chicago.
"We get a goaltender. That gives us three now, so that's a situation that we'll have to deal with," Dallas coach Marc Crawford said after the Stars lost 4-3 in a shootout to the Chicago Blackhawks on Monday night.
The Stars also have Marty Turco and Alex Auld as goalies.
BRUINS 3, SABRES 2 (SO)
In Buffalo, N.Y., David Krejci scored the winner in the third round of the shootout, and rookie Tuukka Rask made 43 saves to help Boston send the Sabres to their fifth consecutive loss.
Daniel Paille scored twice in regulation for Boston (25-22-11).
Derek Roy and rookie Tyler Myers scored for the sliding Sabres (32-18-8).
ISLANDERS 4, PREDATORS 3 (SO)
In Uniondale, N.Y., Mark Streit scored the tying goal in the closing seconds of regulation, and Frans Nielsen and John Tavares connected in the shootout to help the New York Islanders snap a seven-game losing streak.
New York, which hadn't scored during a man advantage the previous five games, connected twice in six chances against Nashville.
HURRICANES 4, PANTHERS 1
In Raleigh, N.C., Joni Pitkanen scored the go-ahead goal, and Manny Legace made 19 saves to help Carolina beat Florida.
Matt Cullen had a goal and two assists, and Tuomo Ruutu and Jussi Jokinen also scored for Carolina.
Cory Stillman scored the lone goal for Florida, which has lost four in a row.
LIGHTNING 3, CANUCKS 1
In Tampa, Fla., Martin St. Louis scored two third-period goals to lead Tampa Bay beat Vancouver.
Steven Stamkos added a goal and an assist for the Lightning.
Vancouver got a goal from Ryan Kesler.
SENATORS 3, FLAMES 2
In Ottawa, Jason Spezza scored his 10th goal in his past 10 games late in the second period to send the Senators over Calgary.
BLUES 4, RED WINGS 3 (SO)
In St. Louis, Paul Kariya scored his first goal at home in more than 15 months and the Blues recovered after blowing a two-goal cushion.
T.J. Oshie and Brad Boyes scored in the shootout for St. Louis.
BLACKHAWKS 4, STARS 3 (SO)
In Chicago, Kris Versteeg scored in the fifth round of a shootout to lift the Blackhawks.
Patrick Kane had two first-period goals for the Blackhawks. Troy Brouwer scored in the third.
Loui Eriksson, Mike Ribeiro and James Neal scored in regulation for the Stars.