“It is strange because Ryan’s peak years seem to have lasted so long,” said Ferguson.

“You would think, at 37, he would be showing signs of waning. I don’t see any evidence of that.

“We look after him in terms of rest before games but when he gets that freshness he doesn’t show any sign of fatiguing at all. He is an amazing man.”

Ferguson virtually ruled Giggs out of Sunday’s crucial Barclays Premier League trip to London to take on Arsenal, when victory would keep them at least six points clear at the top with only three games to go.

Instead, he will keep his longest-serving player in reserve for the return encounter with Schalke, knowing only an improbable three-goal win for the Bundesliga side at Old Trafford will take them through.

For even that very slim hope, Schalke had goalkeeper Manuel Neuer to thank after a performance from the Germany goalkeeper that is the best Ferguson has ever witnessed from an opposition player.

“In my time at United, it is probably the finest display of goalkeeping against us,” said Ferguson.

“I am sure there have been other feats but tonight I saw a very good one.”

The Red Devils chief probably did not know whether to laugh or cry at half-time, so dominant had his side been without getting any reward.

United spurned 11 good chances, then wasted two more after the break before Giggs’ effort was followed, three minutes later, by Wayne Rooney’s 14th of the season.

Ferguson’s side had not conceded an away goal in Europe this season and, true to form, they closed the match out to complete that remarkable defensive record, which left their manager purring.

“Overall I was delighted. It was a top performance,” he said.

“We have had some fantastic performances in Europe during my time.

“Juventus in Juventus in 1999 obviously will always be high on the list but this certainly ranks as one of the best.”