Leonard is officially listed as questionable after "three pretty good days" of practice, coach Frank Reich said Friday.
The linebacker was ruled out for Week 3 last Friday despite getting in a full slate of practices, so his questionable designation today is an upgrade.
Leonard missed the season's first three games while rehabbing from offseason back surgery.
Reich reiterated that if Leonard is able to play Sunday, it won't be at 100 percent. The determining factor in whether Leonard can suit up will be whether he can produce at a high level playing through the injury.
If Leonard can return, it would be a big boost for the Colts' defense against Derrick Henry and the Titans' power-rushing attack.
The Colts defense could be without defensive lineman DeForest Buckner, who is questionable due to a shoulder injury and didn't practice.
Indy ruled out safety Julian Blackmon (ankle) for Sunday's AFC South showdown.