David Beckham has spoken of the challenges Memphis Depay faces in wearing Manchester United's iconic No. 7 shirt.

Former England captain Beckham wore the iconic number for six years for United, between Eric Cantona's retirement in 1997 and his own move to Real Madrid in 2003.

He is part of a proud tradition of players who have graced the shirt, including George Best, Bryan Robson, Cantona and Cristiano Ronaldo.

But since the Portuguese's sale to Real in 2009, United's subsequent No. 7s -- Michael Owen, Antonio Valencia, Angel Di Maria and Depay -- have struggled to have the same impact.

Depay, a £25 million summer signing from PSV Eindhoven, has lost his place and only started one of United's last six games and Beckham believes the No. 7 shirt puts its owner under pressure

"It comes with a huge amount of history: Georgie Best, Bryan Robson, Eric Cantona, Cristiano, it is like No. 10 for Argentina, it is a special number," he said in a news conference. "I was honoured to wear it for the time I did. My boyhood hero was Bryan Robson so it was a huge honour to wear it."

Beckham reiterated that it is not impossible that Ronaldo, who scored 118 goals in 292 games for United, will return to Old Trafford, although he expects him to stay at the Bernabeu.

And he believes the winger's prodigious work rate is one of the reasons why he remains so popular at his former club.

"I always said he is loved by the fans here," Beckham said. "What you have is not just a huge talent but a hard worker. People appreciated that. The way he plays is so special and unique.

"That he is a hard worker sometimes surprises people. He spent a great deal of time here and was very successful but has now gone to Real Madrid, one of the biggest clubs in the world, and I think he is enjoying it there but never say never."