The 27-year-old former Everton front man had the operation at a London hospital on Tuesday afternoon after it became apparent that the problem could not be solved by rest.

A spokesman for the club said: "Duncan had an operation this afternoon in London and will be out for about six weeks."

Ferguson aggravated a long-standing problem during the 4-2 defeat at Liverpool on December 28, but the full extent of the injury did not become apparent until the weekend.

The Scot missed Newcastle's 2-1 FA Cup third round win over Crystal Palace on Saturday as news leaked out that he could be sidelined for up to two months.

Manager Ruud Gullit admitted after the game that an examination this week could mean surgery, and his worst fears have been confirmed.

Ferguson's situation comes as another huge blow to the Dutchman, who is convinced that the club he took over from Kenny Dalglish in August is jinxed.