Paul Scholes believes Wayne Rooney has already entered into decline and could retire in three years' time after being burnt out.
The former Manchester United midfielder played on until he was 38, but believes his long-time teammate could be paying the price for a heavy workload and might be past his peak already.
And while Rooney's current contract at Old Trafford lasts until 2019, Scholes feels the 28-year-old could quit playing before then.
Scholes wrote in his Paddy Power blog: "There's a chance he's worn out. Wayne's peak may have been a lot younger than what we'd expect of footballers traditionally. Age 28 or 29 has been the normal 'peak'. With Wayne, it could have been when he scored 27 league goals in 2011-2012 when he was 26.
"Wayne might be a player who'd retire come 31 or 32, given the amount of football he's played. Ryan Giggs has been on the go for ages, but he adjusted his position. Can Wayne do the same? I don't think Wayne will be able to play centre forward until he's 34 or 35."
Rooney, who will be 29 in October, has already played 517 times for his two clubs, Everton and United, and a further 89 for England, giving him a total of 606 career appearances.
The striker is the third-highest scorer in United's history with 212 goals and Scholes, who also worked him with as part of United's coaching staff for the final four games of the season, feels he will have to do less defensive work if he is to carry on playing.
"His best attributes are his energy, desire, a will to win which is unbelievable -- but, above all, his goals," he added. "Wayne wants all the responsibility to score. He'll try to play left back, right back.
"Sometimes he does that too much instead of saving himself and his energy for what his teams need -- [putting] the ball in the net. He needs to use his energy more effectively now as he's a player who likes to be up front on his own and I don't think he's great with partnerships."