Thomas Vermaelen will be out for up to six weeks after having surgery on his left Achilles yesterday.
The Arsenal defender, who missed eight months last season with an Achilles injury on his right leg, was hurt in the win against Udinese two weeks ago.
Although Arsenal have not confirmed that the 25-year-old had an operation, his father said surgery was carried out in Sweden yesterday.
He told Belgian website Sporza: "The doctor in Stockholm, where Thomas was operated on last time too, recognised the problem now. He would not take any chances and immediately operated on Thomas. He expects five to six weeks of unavailability."
Vermaelen is likely to miss the opening two Champions League group stage games and the north London derby at Tottenham on October 2 which means new signing Per Mertesacker will be thrown straight into action.
