Bryan Robson says Manchester United must do whatever it takes to keep Cristiano Ronaldo at Old Trafford.

The Portuguese wing king is a £35million summer transfer target for Spanish giants Barcelona and Real Madrid.

And speculation that he could leave for the Nou Camp increased when Barcelona director of football Txiki Begiristain was photographed with Jorge Mendes, the 22-year-old's representative, watching Portugal's match with Brazil at the Emirates Stadium on Tuesday night.

Ronaldo has been the key man in United's title challenge this season, netting 15 goals in 23 starts to help them to a six-point lead over Chelsea.

The player himself has admitted he doesn't know where he'll be in six months, but Robson is in doubt United must keep him.

He told The Sun: "It is vital to keep him - he is crucial to United. I don't see any reason why they would let him go. He is contracted to United and has been a massive player for them this season."

Robson does fear the boo boys who heckle Ronaldo at away grounds could drive him out of England.

He added: "I think what may be unsettling him at the moment is that he loves it at United but fans everywhere he goes are booing him.

"Everyone keeps going on about the diving thing but he is playing terrific and maybe he feels he doesn't deserve it.

"But as far as I'm concerned Alex Ferguson will do his best to make sure he remains a United player for the next few years. It's very important."

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