Stamkos, who hasn't played since Nov. 11 due to a surgically repaired broken right tibia, was cleared Wednesday by team doctors.
"I'm excited, a little anxious, a little nervous, everything all in one," Stamkos said. "It's been a long road. It's been tough, but I think this time heading in (to see the doctor) I was the most confident going in there knowing how I felt on the ice, off the ice, what I needed to do in order to get cleared to play, and the tests I needed to go through, and everything felt great."
Stamkos had 23 points in 17 games before the injury and will be part of the puzzle in replacing former captain St. Louis' 61 points, which rank among the top 10 in the league. St. Louis had been seeking a trade after being left off the original Canadian Olympic roster by Lightning general manager Steve Yzerman.
Callahan, a fellow right winger and the Rangers' former captain, has 25 points in 45 games before being shipped to Tampa Bay (34-23-5) along with a 2015 first-round pick and a 2014 conditional second-round selection.
"The Lightning are very excited to have Ryan Callahan join the organization and help us in our quest to make the playoffs," said Yzerman, who praised St. Louis in a statement. "Ryan is an outstanding player and leader who we look forward to seeing on the ice (Thursday) night."
The Sabres (18-35-8) made their biggest deal in the days leading up to the deadline, sending goaltender Ryan Miller and former captain Steve Ott to the St. Louis Blues. However, they made another notable move Wednesday by claiming Cory Conacher off waivers, though it's uncertain if the former Ottawa forward will debut Thursday.
The Lightning just faced Miller on Tuesday in a 4-2 loss at St. Louis. Tampa Bay led 2-0 after the first period with goals from Alex Killorn and Tyler Johnson but would suffer its third loss in four games back from the Olympic break.
They've had the lead in all four games and been outshot 134-88.
"We had multiple-goal leads in three of the four games and we led in every single game, but if you're going to sit here and take 16 shots in one game, 17 shots in another game, 21 shots in another game and expect to win games, it's not going to happen," coach Jon Cooper said. "Unacceptable."
Buffalo had a season-best three-game winning streak snapped Monday in a 3-2 loss to Dallas, the Sabres' first of three consecutive road games.
Enroth made 36 saves against the Stars and has a 3.00 goals-against average in the 2-1-0 span.
The Sabres debuted Chris Stewart, another piece of the trade with St. Louis, at right wing Monday, but the offense came from Tyler Ennis' two goals with Matt Moulson assisting on each. Ennis has four goals in his last three games.
Moulson, who has eight points on a six-game streak, and Cody McCormick were sent to Minnesota on Wednesday in exchange for forward Torrey Mitchell and a pair of second-round draft picks.
The Sabres led 1-0 on Monday after a first period in which they were outshot 16-5.
"(We need) better starts. We got in a hole early," Ennis told the team's official website. "They took it to us. We took penalties and they really dominated us in the first period. Jhonas played great, but we need a better start."
The Lightning posted 3-2 wins in October in their two meetings with the Sabres this season as Johnson had two goals and an assist.