PFA chief Gordon Taylor claims Manchester United stat Wayne Rooney was exploited as a teenager coming through at Everton.
Taylor, chief executive of the Professional Footballers' Association (PFA), suggested what had happened to Paul Gascoigne showed what can go wrong for talented young stars if they are not looked after properly.
Defending his members, he said they were not "cash cows" who lost their principles for money.
And he said Gascoigne, like Rooney regarded by many as the best player of his generation, was now having to come to the PFA for help to keep a roof over his head.
Mr Taylor was giving expert witness evidence at a hearing in which Wayne and Coleen Rooney are being sued by Proactive, the sports agency Rooney signed with in 2003 aged just 17 after signing his first professional football contract with his home town club Everton.
The eight-year deal was brokered by Proactive director Paul Stretford, with the firm getting a 20% commission on sponsorship deals agreed with the likes of Nike and Coca-Cola.
Rooney soon went from an £80-a-week Everton trainee living in his parent's council house in Croxteth, Liverpool, to agreeing £1million-a-year deals with the likes of Nike, the court has heard.
But when Mr Stretford and Proactive parted company on bad terms in October 2008 the commission payments stopped.
Mr Taylor told the hearing, now in its third week at Manchester Mercantile Court, he thought players needed protection and that Rooney had been exploited as he burst on to the football scene.
"I do take exception to players being portrayed as cash cows and having cheques waved under their noses losing their principles," Mr Taylor said. "Someone who has been mentioned, particularly Paul Gascoigne, where now he's in a situation where he comes to us to help provide a roof over his head. Actually I feel he could have been looked after better during his career. I'm not pointing any fingers here."
Mr Taylor was sat yards away from Mel Stein, Gascoigne's former agent, who gave evidence earlier in the day.
Mr Taylor said: "There was a good opportunity to provide for his old age and that's not happened."
The players' union boss said he had known Rooney and his family for a long time and was prepared to give evidence in the case and wanted to make sure he was properly looked after and "not taken advantage of".
Ian Mill QC, representing Proactive, asked Mr Taylor: "You came here with the preconception Proactive has abused its position with regard to Mr Rooney?"
Mr Taylor replied: "He could well have been. Having looked at the evidence I have great concerns at certain arrangements that were made as a youngster at 16."
The witness said his job was to ensure young players were not exploited; that on average players have a career lasting just eight years and must use that time to "capitalise on their abilities".
He said of the 600 players who get professional contracts aged 16, just 100 are still in football aged 21.
Mr Mill continued: "Is it your view, having studied the evidence, that Proactive exploited Mr Rooney in the arrangements made in 2003 or not? Yes or no?"
Mr Taylor replied: "If you wanted me to say yes or no, I would say yes. I don't think eight years was reasonable. With regard to the terms, we have already heard evidence it was impossible to get out of his contract during the eight years.
"I didn't think that was the world I wanted to create for footballers. He clearly feels he's not been treated fairly because he wants this particular adviser against the company you are representing."
