Fisher said Young has a torn flexor tendon in his right thumb that requires surgery. The signal-caller sustained the injury during Sunday's loss to the Washington Redskins.
"Our medical staff is recommending surgery ... and that would indicate his season is over. In the next day or so we are going to put him on injured reserve," Fisher said. "Our doctors said ... that it needs to be fixed. So that's what we're going to do based on the recommendation."
Young had been stripped of his starting job by Fisher after the Washington game, reportedly following a verbal altercation between the two in the locker room.
Rookie Rusty Smith is set to assume the Titans' starting quarterback job.
Young was enjoying his best year with a 98.6 quarterback rating in nine games, throwing for 1,255 yards and 10 touchdowns with three interceptions.