In an Instagram video from Omar Kelly of the South Florida Sun Sentinel, Dolphins head coach Adam Gase announced Tannehill would have a second opinion and noted that "everything is on the table" for his quarterback right now.
Tannehill injured his knee during practice at training camp on Thursday when he fell to the ground on a non-contact play.
There was some hope it wasn't serious when NFL Network's Aditi Kinkhabwala reported Tannehill suffered no structural damage. ESPN's Adam Schefter reported there was "fear" within the Dolphins organization that Tannehill would need surgery that would end his 2017 season.
The 29-year-old suffered a partially torn ACL in his left knee during a Week 14 win over the Arizona Cardinals. He missed the Dolphins' last three regular-season games and the AFC Wild Card Game against the Pittsburgh Steelers.
Backup quarterback Matt Moore, who started in place of Tannehill after his injury last season, will take over first-team snaps with the offense for the time being.