Winger Ronaldo has scored 18 goals this season

Real Madrid would like to sign the 22-year-old and Barcelona have also been linked to him, although Ronaldo has insisted he is happy at United.

"They link themselves to whoever they feel fit and it's not right," United legend Charlton told BBC Five Live.

"I don't think it's a correct way to go about their business."

I can see no reason at all why he should want to play for another club Bobby Charlton on Cristiano Ronaldo

Ronaldo's form for United this season has helped fire them to the top of the Premiership but has also seen him linked with a move to Spain.

Real president Ramon Calderon told a Spanish TV station last month: "We really like him but he belongs to Manchester United and they have to decide to sell him first.

"If that is the case then we'll be first in the queue."

But Charlton is confident Ronaldo will stay at Old Trafford, with the young Portugal star already holding talks about his extending his contract until 2012.

Charlton added: "I can see no reason at all why he should want to play for another club.

"It's really destabilising for both the club and the player to have all this speculation about his future. All of it is coming from abroad and none from our club."