Coming within weeks of Roy Keane’s sensational departure, it brought huge pressure on Sir Alex Ferguson, with many pundits claiming it was time the Scot’s illustrious 19-year reign was brought to an end.

Fans have even spoken to Charlton, questioning Ferguson’s tenure. Yet the former England skipper, one of only two Englishman to win both the World Cup and European Cup, is adamant Ferguson remains the right man for the job.

“The criticism of Sir Alex has been quite unfair,” Charlton told MUTV.

“He has done the best he could with the players he has had.

“In some ways, you could say the transfer window has worked against him because it has stopped him trying to solve a problem.

“But he is still a great manager and motivator and if you took away Chelsea, we would not be doing too badly at all.

“It is a disaster we are not in Europe but I have no worries about Sir Alex Ferguson or the future of Manchester United.”

Charlton was in Lisbon the night United’s Champions League dream imploded with a defeat to Benfica and admits he struggles to explain how it happened.

That the loss came within a period where United have picked up 19 points from their last seven Premiership outings just makes it even more remarkable, although overall Charlton admits Ferguson’s side did not do enough to get through.

“We had a lot of trouble scoring goals on those European nights,” said Charlton, who is still a member of the football club board.

“There were a couple of games when I don’t think we even had a shot.

“I am certain Sir Alex will put his thinking cap on and work out why it happened, how it happened and how we can put it right.

“I really don’t know what it was. I wish I did. Maybe the opposition did not motivate the players enough, I really don’t know.

“What I do know is that Manchester United do not have a divine right to qualify.

“Hopefully the players will learn from the experience and the next time they have the opportunity to play in Europe they will look back at this season and remember what can happen if you do not give it 100%.”

Although he is disappointed at the European failure, Charlton’s spirits have been lifted at the recent return to form on the home front.

With a Carling Cup semi-final to look forward to and a surge up the table taking United into second spot, even if they remain nine points adrift of leaders Chelsea, the Old Trafford picture suddenly looks much brighter than it did a month ago.

And, in Wayne Rooney, Charlton believes United have the most exciting player in the English game, a man he eventually feels will be regarded in the same manner as his old team-mates George Best and Denis Law.

“Just like George and Denis, Wayne gets me off my seat when he gets the ball and there are not many players who can do that,” he said.

“He is such a marvellous player to watch, yet it all seems so effortless.

“I am so pleased we have him at Manchester United. There is no question he will go on to become one of the great players. He has a God-given talent and you can just see how much he loves the game.”