Even as his team prepare to raise the curtain on the new top-flight season tomorrow, Sir Alex Ferguson remains misty-eyed about the star performer who has left the building.

Other big-name players have departed the Old Trafford stage with barely a pat on the back from Ferguson down the years, but the Manchester United manager continues to shower bouquets on Cristiano Ronaldo.

The context yesterday, before the Community Shield match against Chelsea at Wembley tomorrow, was the size of the task facing Wayne Rooney, in particular, as he looks to lead United into the post-Ronaldo era. For all the varying qualities of Dimitar Berbatov, Michael Owen, Antonio Valencia and others, Rooney appears the most obvious talisman for the new-look United, but Ferguson appeared hesitant at best yesterday when asked whether the England forward was ready to emulate Ronaldo, now at Real Madrid, in making the jump towards the highest echelons.

It was put to Ferguson that three years ago Ronaldo and Rooney were synonymous, two young players, 21 and 20, with immense potential and that, whereas the Englishman has gradually attained or come close to world-class status, his Portuguese team-mate went stratospheric.

Greatness should not be measured in terms of goals alone, but, having scored as many Premier League goals (13) in his first two seasons at United as Ronaldo managed in his first three, Rooney, like everyone else in the English game, was left in Ronaldo’s wake from the start of the 2006-07 campaign, managing 38 goals in 83 league starts as opposed to his team-mate’s incredible haul of 66 in 93.

When Ferguson described Ronaldo recently as “without question the best player in this world of ours — streets ahead of Lionel Messi, streets ahead of Kaká”, it went without saying that he was saying that Real’s ￡80 million man was streets ahead of anyone he left behind at Old Trafford. That extends to Valencia, who was signed from Wigan Athletic as the closest thing to a direct replacement for the Portugal forward, but Ferguson is expecting big things from the Ecuadorean, a more orthodox threat on the right wing, as well as a great leap forward from Rooney and others.

Ferguson talked of having “bought potential” in the shape of Valencia, a player who, having turned 24 this week, is only six months younger than Ronaldo. He talked, too, of the rich potential of Rooney, Nani, Danny Welbeck and, in particular, Federico Macheda, the 17-year-old Italian forward who, he said, “is going to give me real problems. For his age, he’s exceptional. He’s going to be a top, top player.”

No one at Old Trafford, it seems, though, can yet bear comparison to Ronaldo. “Wayne is a totally different type of player to Ronaldo,” Ferguson said. “I don’t think you can compare them. Ronaldo is lightning quick, he has two good feet, he is magnificent in the air, and what is there left to say about his goalscoring record?

“For any player, whether it is Rooney, Macheda, Welbeck or Nani, all the forwards, they all have to say, ‘Well, this guy was exceptional.’ And the only way any player can achieve an improvement is through practice on the training field, having the desire to improve themselves in every training session. People in our game misread what a training session means. It’s not just to fill your morning or keep you out of the house. It is to improve yourselves as footballers.

“We are lucky that some of the players we have had here, and have at the moment, have that desire to improve all the time. It’s only through training sessions that players can improve.”

What is clear is Ferguson’s belief that Ronaldo rose to greatness through hard work and that nobody, whether it is Rooney, Macheda, Berbatov or Nani, can expect to emulate their former team-mate without total commitment on the training ground.