Sir Alex Ferguson launched a passionate defence of his fellow managers as he prepared Manchester United to face Liverpool in the Premier League.

Liverpool have failed to challenge United, Arsenal and Chelsea for the championship and Ferguson believes question marks over Rafa Benitez's position at Anfield, where the club's owners admitted an approach to former Germany coach Juergen Klinsmann, may have undermined their cause.

"I don't think it helps. I don't think any media attention helps when the manager is being criticised," Ferguson said.

Ferguson, who has been in charge at Old Trafford since 1986 and has always been a staunch supporter of the League Managers' Association, said the current debate over criticism within football should extend beyond referees to take in managers.

"There is talk of criticism of referees but no-one gets criticised more than managers - the humiliation managers endure every season.

"The rapidity of managers being sacked this season is at an all-time peak, particularly in the Premier Division.

"Every Christmas time there are a third of managers in the country wondering about their jobs and going home to tell their kids they haven't got a job.

"That's the humiliation managers face every time."

Eight Premier League clubs have changed manager this season, including Chelsea who play Arsenal in the later kick-off on Sunday.

United are looking to extend their three-point lead at the top of the table against Liverpool, who are fourth, by notching a seventh win in eight meetings between the clubs.

"We are first on the menu and the nature of our football business is we hope we win our match and we can then sit and think about what's the best result in the other match," Ferguson said.

"But I think the three of us involved in this race have got difficult games and no-one can say they are certain to win it."

Nemanja Vidic will be fit for United despite coming off with a nose injury in Wednesday night's win over Derby County but Rio Ferdinand and Edwin van der Sar face fitness tests.

Mikael Silvestre made a successful comeback following seven months out with a knee injury with a 75-minute appearance in the reserves on Thursday when Gary Neville completed the full game.

With Neville close to full fitness, Ferguson has allowed right-back Danny Simpson, 21, to join Championship club Ipswich Town on loan for the rest of the season.

Meanwhile, United have confirmed the appointment of former club captain Bryan Robson as a global ambassador for the club. Robson was out of work after an ill-fated spell as manager of Sheffield United ended after less than eight months.

Reuters