Charlton, an Old Trafford director, is uniquely qualified to discuss the quality of footballers to have played for United after over half a century associated with the club.

Having spent the most productive years of his club career alongside players of the calibre of Denis Law and George Best, Charlton is no stranger to prodigious football talent, yet the England World Cup winner confesses that even he has been stunned by Ronaldo's superlative form this season.

United manager Sir Alex Ferguson has confirmed the club are progressing with talks designed to hand Ronaldo an improved contract, even though he is already tied to the team until 2010, and Charlton is certain they have a unique talent on their hands.

"Ronaldo has just been fantastic," said Charlton. "It takes great players to grab the bull by the horns and lift people and he has been doing that recently.

"He does things I have never seen anybody else do. And the one thing he does do is he is as tough as hell. If you clatter him, it doesn't bother him too much, he'll carry on. His goal at Fulham was just marvelous and I think he has been a better player than even people here realise."

Charlton also leapt to the defence of Ronaldo, who is still accused of diving in search of penalties. The latest such incident saw the United star harshly booked for a supposed dive as he bore down on goal during United's Champions League victory over Lille on Wednesday.

"He doesn't do that normally," said Charlton. "Why would he? If he is getting near goal and he's given the chance, what would he rather have, the penalty or the goal? He will always go for goal, he is such a strong character."

Charlton was talking before United's Champions League draw pitted them against Roma in the quarter-finals and, as the club prepares to celebrate its 50th anniversary in European football by playing a European XI in a charity fund-raiser on Tuesday, Charlton believes success in the competition for the first time since 1999 is overdue.

"A lot of people have said that Alex has not won as many European Cups as maybe he should have, considering the number of times he has won the title," said Charlton. "For him, it would be marvellous, for the whole club, really.

"It is the biggest prize and yes, absolutely, the club should have had more European Cups and Alex desperately wants another European Cup. But he desperately wants another Championship, another FA Cup. He is what he is, he does what he does every day and never changes.

"The first thing Alex Ferguson ever said when he came here was that winning the championship was the only thing to do. That has never changed."

Charlton, a member of the first United team to win the European title in 1968, also believes the signs are that his beloved Reds are capable of doing so for a third time.

"When you get to this stage of the season, things tend to settle down a bit," said Charlton. "A lot of the trepidation you had about your form and your team back in September and October is gone. When you start getting through to the second stages, anything can happen.

"It's a pleasure to watch this team. The last few weeks they maybe have not been playing as well as they were earlier in the season but they have still been winning. When you start winning on a regular basis you start believing that nothing is beyond you."