Tennessee Titans quarterback Marcus Mariota is not expected to play on Sunday night against the Indianapolis Colts because of a nerve condition caused by a “stinger,” Chris Mortensen of ESPN reports.

Mortensen also goes on to report that Mariota’s playing career could also be in jeopardy due to the injury.

Mariota is officially listed as questionable and reportedly will test his arm in pre-game warmups. But one source told ESPN that an independent spine specialist has warned the Titans that further damage will put Mariota's ability to throw the football at significant risk beyond this weekend.

With Mariota unlikely to go, Blaine Gabbert will get his third start of the season. Austin Davis, whom the team signed this week, will likely be Gabbert’s backup.

In his seven appearances this season, Gabbert has completed 60 percent of his passes for 461 yards with three touchdowns and two interceptions. The Titans won both of his starts this season, although he made way for Mariota early in their win against the Jags.

Mariota’s absence is a huge blow for the Titans, who need to beat the Colts in order to win the AFC South and make it to the playoffs. And if they lose, they will be out.

But more importantly, though, they should also be concerned about Mariota’s long-term future. As one source told Mortensen, an independent spine specialist said, “it is the physical contact of a football game that would subject Mariota to the risk of permanent damage.”

Even if the Titans beat the Colts and make the playoffs, they have some big decisions to make regarding Mariota in the playoffs and moving forward given his serious medical situation.