The Dolphins placed Tannehill on injured reserve Saturday because of his left knee injury, sidelining him for the entire season. Tannehill and the Dolphins decided surgery would be the best option for his torn ACL.
When asked about his conversation with Tannehill, Gase said: "It was probably tougher for me. It's more and more real. It's unfortunate for him. He worked so hard."
Tannehill initially injured his left knee in December against the Arizona Cardinals, partially tearing the ACL. It was reinjured Aug. 3 on a non-contact play, when Tannehill crumbled to the ground while scrambling in practice.
Tannehill's $17.98 million salary for this year is fully guaranteed, but only $5.53 million of his $17.48 million salary for 2018 is guaranteed against injury. He has no guarantees other than that, which means the Dolphins could move on from Tannehill after this year with little financial commitment.
"If he feels good enough to go on Thursday, where the pocket feel is there and he feels like he's in a good place, then he'll go," Gase said.
Cutler, who parted ways with the Chicago Bears in May after eight seasons, postponed retirement and his TV job to sign a one-year, $10 million contract last week with the Dolphins.
Tannehill will still be around the team this season, Gase said.
"There are going to be times where he'll be rehabbing at other facilities," Gase said. "But there will be some weeks where he's going to be around a lot, and he'll be able to help the coaching staff and help the players."
To fill Tannehill's roster spot, Miami signed linebacker Junior Sylvestre, who spent part of the 2017 offseason with Buffalo and the 2016 offseason and training camp with Indianapolis.
Tannehill, who made 77 consecutive starts before his injury last season, chose to avoid surgery after last season's injury. He instead rehabilitated the partially torn ligaments and underwent stem cell treatments.
Information from ESPN's Dan Graziano and The Associated Press was used in this report.