England captain Michael Vaughan has been ruled out of the Ashes tour of Australia after a fourth operation on his right knee, the England and Wales Cricket Board (ECB) confirmed Thursday.

The Yorkshire batsman went under the knife on Monday still clinging to the hope that he could be fit in time to lead England on the tour, which begins in November.

But according to the BBC, the surgery revealed more extensive damage to the joint than expected -- a development, which will intensify fears, that Vaughan's career could effectively be over.

However, after an ECB spokesman confirmed that Vaughan would miss the Ashes tour, David Graveney, England's chairman of selectors, told BBC Radio Five: "There is no suggestion that

Michael Vaughan's career is under threat."

Vaughan has not played for England since being forced to return home early from the tour of India in March.

He attempted a comeback for Yorkshire last month but the injury flared up again and he was advised that further surgery was necessary.

Vaughan last year skippered England to their first series victory over Australia in nearly two decades and had been desperate to lead the side's bid to retain the Ashes.

The news that their 31-year-old captain is to miss the Ashes, which start in November, will come as a huge blow to England whose Test series triumph over Australia under Vaughan's captaincy last year was their first since 1986-87.

Vaughan's knee injury flared up again during Yorkshire's County Championship match away to Sussex at Arundel last month, where he was unable to field for much of the game.

That led him to see a new specialist where it was decided he needed an operation to repair damage to the articular cartilage in his right knee.

England have used four different captains since November 2005 and opening batsman Andrew Strauss is set to lead an injury-hit team in next week's first Test against Pakistan at Lord's.

But England hope all-round star Andrew Flintoff will return from an ankle problem to captain the team in the second Test at his Old Trafford home ground later this month and lead England in November's first Ashes Test at Brisbane.

Following the news that Vaughan had been ruled out of the Ashes, leading British bookmakers William Hill lengthened the price of England winning the series from 3/1 to 4/1.

Australia were shortened from 8/11 to 1/3 with a drawn series now offered at 5/1 while the hosts were 8/1 to whitewash England 5-0.