The 39-year-old Argentinian ruptured his left Achilles during Sunday's 1-0 Serie A defeat at Palermo and went under the knife at Pavia's Policlinico San Matteo on Tuesday afternoon.
Professor Franco Benazzo, who performed the operation, told Inter's official website: "The operation was a complete success.
"How long will it take him to recover? He'll have his foot in a cast for the next three weeks and won't be able to walk on it, then he will start to walk in phase two of his physiotherapy.
"As ever in cases like these we're looking at six months out of action."
Benazzo added: "Is there a chance he might lose a bit of fitness after an operation like this? In general terms no, but locally the muscle mass will decrease slightly during the time his foot's immobile.
"But the Inter medical staff have shown over the years that they can get players fit who have suffered from more serious injuries than a snapped Achilles."