Stamkos, who can become an unrestricted free agent July 1, was offered an eight-year, $68 million contract extension by the Lightning, Sportsnet's Elliotte Friedman reported Saturday.
Callahan said Stamkos has worked hard to keep his contract status from becoming a distraction this season.
"We haven't talked about it," Callahan said. "It's part of the business. It's something that's not really discussed among the players. Everybody has to go through it at some time or another, and obviously there's different players that it gets magnified. But he's been great. He's a pro about it. He's been in the League for a while, and I think he understands that. All the guys in here support him."