Fleener has been out since Tuesday with a concussion. Head coach Chuck Pagano wouldn't say when the injury occurred, although it's likely sometime during Sunday's game against the Buffalo Bills.
The Colts are already hurting at the tight end position with starter and fellow second-year player Dwayne Allen sidelined. Allen has a foot injury that is expected to keep him out for the majority if not all of the preseason schedule.
In Fleener's rookie season last year, the youngster racked up 26 catches for 281 yards and a pair of touchdowns. In comparison, Allen had 45 receptions for 521 yards and three scores.