The Black Cats today confirmed that the 28-year-old Scotland international had an operation in Sweden yesterday.
Manager Steve Bruce told the club's official website, www.safc.com: ''Craig had the operation yesterday and it went well. He will be out for about four to six months now.''
Gordon had travelled to Scandinavia to consult renowned specialist Professor Hakan Alfredson for the second time in the hope that surgery could be avoided.
He had earlier been given a programme of exercises designed to strengthen the knee by Prof Alfredson.
However, as Bruce had hinted on Friday, it was obvious that there was no alternative once the second examination had taken place and the decision was taken to carry out the operation.
Bruce added: ''Craig's been following a programme, but when the specialist had a look at the knee again, we were left with no choice but to go ahead with the surgery.
''That just sums our luck up at the moment.''
The news will have come as a blow to Bruce, who said in the wake of Saturday's 2-0 Barclays Premier League defeat at Birmingham that plans for Gordon's operation, if necessary, would be put on hold until the end of the season.