The team announced the decision about three hours before kickoff.
Bortles, the third overall pick in May's NFL draft, sprained his right foot Sunday at Baltimore and was limited in three light practices since.
The rookie was officially listed as questionable, and coach Gus Bradley said he would be put through pregame mobility tests before the Jaguars (2-12) determined his playing status.
The team says his foot feels good enough to play against the Titans (2-12).
Bortles has 10 touchdown passes and an NFL-high 17 interceptions this season. He has been sacked 46 times.