While Tannehill could have decided to rest the knee for six to eight weeks and try to come back from the injury again, surgery was the most viable and likely option.
Tannehill initially injured the knee in December against the Arizona Cardinals, partially tearing the ACL. It was reinjured Aug. 3, on a noncontact play, when Tannehill crumbled to the ground while scrambling in practice.
The Dolphins and quarterback Jay Cutler agreed to a one-year, $ 10 million deal on Sunday. In May, Cutler had retired from the NFL and was hired by Fox Sports as a game analyst, but he is putting that off for a year.
Dolphins coach Adam Gase played a significant role in convincing Cutler of the reasons he should play for the Dolphins.
Cutler, 34, started 15 games in 2015 with Gase as his offensive coordinator, throwing for 3,659 yards with 21 touchdowns and 11 interceptions. He completed 64.4 percent of his passes.
Last season, Cutler played in just five games because of thumb and shoulder injuries. He suffered a torn labrum in his right throwing shoulder and underwent surgery in December.