Tannehill, who missed the past five games with a capsule injury in his right shoulder, threw the ball in practice Tuesday for the first time since Week 6. He completed 25- to 30-yard passes to receivers running a variety of routes; he showed no apparent sign of discomfort or injury.
"I'm not quite 100 percent, but I feel confident and have made all the throws that I'm going to need to make over the course of the game," Tannehill said. "I don't feel like any aspect of my game has been taken away."
Three weeks ago, Tannehill said he felt a stabbing pain in his shoulder. But this week, he says that pain has been minimized.
Tannehill said he hasn't had to change his throwing motion, which was significant to avoid other problems going forward, and throwing reps haven't been an issue. His keys going into Sunday are playing fast, getting the ball out on time and trusting his offensive tackles.
"He was ready to go. He's been waiting for this week to come for a while," Gase said. "The whole thing was making sure he stayed patient and with the program. ... We had a good week last week, and [Tuesday] was a good start for us with him practicing the whole practice."
Gase told Tannehill and Brock Osweiler of his decision Monday night. Gase's decision was confirmed after watching Tannehill complete an entire practice on Tuesday.
"I thought he looked good," Gase said. "It's always going to take time. It's a little different receiving corps that was out there today than when he left."
Tannehill, who was injured during the Dolphins' loss to the Bengals on Oct. 7, is spending significant time with trainers before and after practice to get loose and maximize his effectiveness on Sunday.
The Dolphins, who haven't scored an offensive touchdown since Oct. 25, believe Tannehill's return will help lift their offense. He went 3-2 as the starter. Osweiler went 2-3 as a starter replacing Tannehill.
"It's been a hard five weeks of sitting out, sitting back, itching and biting at the bit," Tannehill said. "To finally be healthy enough to go and be with my guys, I'm really excited and looking forward to the opportunity."
Miami, at 5-5, is tied for the AFC's No. 6 playoff spot with five other teams, including Indianapolis.
Several Dolphins players seemed energized in the locker room by Tannehill's return, and felt it could help propel them in their playoff push.
"Tannehill is very smart, he's tough. When it's third down, he can get out some stuff and run to get the first down. They have to be aware of that," running back Frank Gore said. "He knows how much we need him. He knows he'll be in pain, but you can tell he wants to play. That's a plus for us."
There's no guarantee that Tannehill won't have a setback, and he indicated last week that he believed he would have to play through pain for the rest of the season. He said Tuesday he's not sure if that has changed. Gase said Tannehill hasn't told him about any pain this week and that his recovery has been positive. Gase told Osweiler to stay ready to go just in case.
Tannehill said after getting the MRI in Week 6, four or five doctors were all on the same page going forward and everyone's confident that "no further injury is going to be caused by playing through it."
Gase said Monday that Tannehill has increased his throwing program to passes up to 50 yards with trainers and that he's able to make awkward throws and throws on the move.