Adam Schefter says Titans QB Marcus Mariota is not expected to start Tennessee's Week 17 matchup against the Colts due to a nerve condition. (1:06)

Mariota not expected to start with playoffs on the line (1:06)

Tennessee Titans quarterback Marcus Mariota won't play Sunday night against the Indianapolis Colts primarily because of a nerve condition caused by a stinger, which has his overall playing status in jeopardy, sources familiar with his injury told ESPN.

One source told ESPN that an independent spine specialist has warned the Titans that further damage would put Mariota's ability to throw the football at significant risk beyond this weekend.

Blaine Gabbert will start in Mariota's place against the Colts in a AFC South game in which the winner will advance to the playoffs and the loser will be eliminated. The Titans also signed free-agent quarterback Austin Davis this week, and he likely will be the backup quarterback against the Colts.

The Titans are hopeful that the nerve trauma will diminish with more rest and allow Mariota a chance to play in the postseason, a source added.

A team spokesman did not have an immediate comment.

Mariota was listed as a limited participant in the Titans' practice this week and was given a questionable status on Friday's injury report with stinger and foot issues. He was observed throwing the football by media during open portions of practice.

But one source said that it is the physical contact of a football game that would subject Mariota to the risk of permanent damage, according to the opinion of the independent spine specialist that has been shared with team officials and the medical staff.

Mariota's foot injury is a partially torn plantar fascia, a source added.