Paul Hayward told the Sunday Supplement that Manchester United and England striker Wayne Rooney is at a crossroads in his career.
Rooney, 26, is currently out injured after he suffered a deep thigh wound in a challenge with Fulham's Hugo Rodallega.
In his absence, United's new signing Robin van Persie scored a hat-trick against Southampton while England scored five goals against Moldova in their opening World Cup qualifier.
While Hayward believes Rooney will return as an extremely good player, he says the forward must rededicate himself to the game if he is to become a great footballer.
"We always talk about crossroads in this industry and it's a bit of a cliché but he really is at one this year, I think.
"His international career has stalled pretty much and in his club career he has already gone beyond the line of us thinking that he could be a Messi or a Ronaldo.
"The crucial difference between him and them is the physical shape he's in and the fact that he has to battle his body a lot of the time, it seems.
"I think he's picking up more and more minor injuries. I don't think physically he's sometimes in the shape that he should be, as he admits in his own book, actually.
"The book betrays a lot of doubt and uncertainty and it's quite candid in the sense that he's admitting to being a guy who struggles with himself, his body and his form sometimes.
"What we're talking about is the difference between and extremely good player and a great player. He's an extremely good player - one of the best this country has produced.
"But we're still wondering whether he is going to go on and be a great, great footballer of the stature of Platini, Messi or Ronaldo. He can only give himself a chance of doing that if he makes the right choices.
"I just think he has to completely rededicate himself to the game and say 'there's only one thing that matters now - and that is fulfilling my potential'."
According to the Sunday Mirror, Rooney could once again team up with Cristiano Ronaldo at United if the 27-year-old Portuguese winger does indeed want to leave Real Madrid.
Last week Ronaldo - who joined Real in an £80m deal from United - admitted that he is unhappy with the club and refused to celebrate his goals in the win over Granada.
Hayward told the Supplement that 'ultimately' Ronaldo's decision would be financially motivated.
"Talking about Rooney, Ronaldo was a very precocious player as well," he said. "Rooney hit the top at 16 or 17, which is going to give you a problem in your mid-twenties unless you plan and adjust.
"Ronaldo hit the top around about the same age with Sporting and look at him now - he's a magnificent athlete.
"The Real Madrid crowd didn't really take to him initially because he was trying to win games on his own in that team. He played on his own in that team - he thought 'this team isn't as good as me, I'm just going to run with the ball and shoot and not pass to anyone'.
"He's modified that a bit; the team has grown up around him and become more successful. You'd fancy them to win the champions League this year in many ways, so he's not the standout 'messiah' figure any more, I don't think.
"He's the best player in a very good team - probably the best team in Europe. I don't think he likes that particularly but I'm sure ultimately he's looking at the sums.
"If he went to the French League, for a player of his quality he's retiring in league football anyway, because their league is not on the same level."