Duncan sustained the injury on a non-contact play while returning a kickoff in practice on Tuesday.
Duncan, a redshirt sophomore, played in 11 of 12 games last season and started nine of them. He was competing for a starting role this year after logging 28 receptions for 441 yards with four touchdowns. Only Steven Scheu, an All-SEC junior tight end in 2014, had more receiving yards than Duncan with 525.
“I know C.J. is disappointed with the injury, and we share his disappointment,” Mason said. “He's one of our most versatile and proven offensive performers, but even more than that, C.J. is very much a team-oriented player. As he recuperates, C.J. will be an encouraging and helpful presence to the receiving corps.”
Vanderbilt was shut out in conference play last year, going 0–8 against SEC opponents and finishing with an SEC-worst overall record of 3–9.
The Commodores begin their 2015 season on Sept. 3 against Western Kentucky.
- Erin Flynn