Duncan hurt his leg during special-teams drills near the end of Tuesday afternoon's practice. Vanderbilt coach Derek Mason announced Wednesday that the injury likely will knock Duncan out for the whole season.
Duncan, a sophomore from Montgomery, Alabama, caught 28 passes for 441 yards last season. He started nine games and tied for the team lead with four touchdown catches.
Mason called Duncan ''one of our most versatile and proven offensive performers, but even more than that, C.J. is very much a team-oriented player.''