Manchester United boss Sir Alex Ferguson's determination that his players not cash in on their off-field profile was key to Cristiano Ronaldo seeking a move to Real Madrid, it has been claimed.

It is a scenario that echoes the experience of David Beckham, whose departure to Real Madrid in 2003 was influenced by Ferguson's view that his off-field profile was distracting focus from the team.

Mary-Ellen Field, a leading expert in commercial and licensing rights, told Observer Sport: "Ferguson's view that [commercial exploitation] takes a player's mind off the game is valid.

"However, the contract between the player and licensee means they usually have to work 20 days a year at most.

"With any brand building, whether it's a person or product, the more positive exposure you get, the more valuable your brand becomes. It would have been beneficial for the club and player to get as much exposure as possible."

In 2002, United signed a 13-year £300m contract with Nike that allows the company to control the club's ­global licensing and retail operations. believes that if Ronaldo had been able to develop, for example, his own perfume brand, like Beckham's lucrative Pure Instinct, it would have been mutually favourable.

Despite being the world and European player of the year, Ronaldo's only major deal is a recent agreement with Castrol, in contrast to Beckham's blue-chip partnerships with Armani and Adidas.

"There is no downside. The player is happy with his endorsements, and the club can sell the product and get the mark-up - website sales are huge," Field said.