NASHVILLE, Tenn. -- The Titans will "very likely" be without starting quarterback Ryan Tannehill for the remainder of the season due to a right ankle injury that is likely to require surgery, sources confirmed to ESPN on Wednesday.

Tannehill suffered the injury Sunday, when Los Angeles Chargers outside linebacker Khalil Mack landed on his right foot on Tennessee's first offensive drive.

Team trainers took Tannehill to the locker room on a cart. The quarterback missed only one offensive series and returned to the game with his right ankle heavily taped.

"We are never going to question his toughness or his willingness to get back and help us win," coach Mike Vrabel said of Tannehill following the Titans' 17-14 loss.

The injury was to the same ankle Tannehill injured in Week 6 against the Indianapolis Colts. Despite finishing that game, Tannehill missed the following two weeks, with backup QB Malik Willis starting in his place.

Willis took all of the first-team snaps in practice on Tuesday and Wednesday. The Titans, who currently lead the AFC South at 7-7, also signed veteran quarterback Joshua Dobbs to the active roster on Wednesday.

With Tannehill unable to play, Dobbs would slide in as the backup with Willis as the starter.

The 7-7 Titans' lead atop the AFC South, the division they've won the past two seasons, has dwindled to one with a four-game skid. They host the Texans (1-12-1) on Saturday -- the same team Willis made his first NFL start against Oct. 30 in a 17-10 win. Tennessee closes the regular season at home against the Dallas Cowboys and on the road at Jacksonville.

Tannehill has thrown for 2,536 yards and 13 touchdowns with six interceptions this season. NFL reporter Paul Kuharsky was first to report him likely being done for the season.

Tennessee on Wednesday also placed offensive lineman Dillon Radunz on injured reserve because of a knee injury suffered in Sunday's game against the Chargers.

Information from The Associated Press was included in this report.