The 29-year-old had an operation on Thursday on the injury that flared back up in the FA Cup replay win at Fulham earlier this month, and has been ruled out for a minimum of 12 weeks.
Black Cats boss Gus Poyet confirmed the loss of the Italian – who played a key role in his side’s successful survival mission from the bench last season – but said surgery was the only option.
Poyet said: “He (Giaccherini) was like a new player in pre-season – he came back really strong and started the new season very well.
“Then he got an injury which took him a while to come back from, and when he was coming back he got another kick in the same place which made the medical staff take the decision to have the operation.
“Towards the end (of last season) when we did the miracle he was a very, very important player – he was coming from the bench and changing games.
“It’s tough but I think it’s the risk of forward players. We need to be sure he is 100 per cent and we wish him well and hope he will make a full recovery.”
Poyet has a number of injury concerns ahead of Saturday’s trip to Manchester United, with Billy Jones, Jack Rodwell and Will Buckley all battling to be passed fit.