As the most obvious link to the start of United's 50-year European adventure, which will be celebrated by a UEFA-backed charity game at Old Trafford on Wednesday, Charlton is well placed to judge the merits of those who have come before Ronaldo.

With George Best and Denis Law among his former team-mates, as well as the talents of Duncan Edwards, Tommy Taylor and Eddie Colman which were all lost in the 1958 Munich disaster, Charlton is no stranger to players of great ability.

Yet he believes Ronaldo stands alone and confidently predicts the Portugal winger will go on to become a Red Devils legend.

"Cristiano is unlike any other player we have seen at this club," said Charlton.

"I cannot compare him with anyone. He is faster and stronger and does things with a ball most people can only dream about.

"He is a quality player at the highest level and potentially, he is one of the greats."

Although few would describe Ronaldo as a leader of men, Charlton has been impressed by the 22-year-old's desire to take responsibility.

Never has that been more in evidence than over the last two weeks, when his solo goal earned United an unexpected victory at Fulham before he embarked on the touchline gallop against Lille on Wednesday and then provided the cross that set up Henrik Larsson for the goal which earned the Red Devils a quarter-final meeting with AS Roma.

"I don't think it is intentional but he leads by example," said Charlton.

"At Fulham, he literally won the game for us on his own. He lifts the team and a lot of important goals and build-ups come from him.

"If things are going wrong, you sit in the stands hoping someone can turn the corner and change things for us. He is a player who can."

It is because of the presence of players like Ronaldo and Wayne Rooney that Charlton firmly believes United can mark their half century of European combat by winning the tournament for a third time.

Should United emerge victorious from their meeting with Roma, a mouth-watering two-legged encounter with either AC Milan or Bayern Munich awaits.

Both sides have eclipsed United in terms of tournament victories, with Charlton agreeing with the verdict of Sir Alex Ferguson that the Old Trafford outfit have underperformed in the competition.

"We should have done better in the European Cup," he admitted.

"Our own side had chances in a couple of pressure semi-finals but unfortunately, we missed the boat.

"But I don't see why we cannot win it this year. There is nothing quite like getting on a run of good results to build confidence.

"Providing we can avoid injuries and silly mistakes, we have the players who can score against anybody, so I do not see why we should be frightened of any opposition."