Green went under the knife to repair the muscle he ruptured during England's B international at Reading last Thursday. Canaries physiotherapist Neal Reynolds said the operation had gone well and gave the first real indication of how long Nigel Worthington can expect to be deprived of his number one.
"Robert is recovering well all things considered," Reynolds told the club's official website. "He will be on crutches for the next two to three weeks and then it's a case of sitting down and working out his rehabilitation programme moving forward.
"The original assessment that he is likely to miss the start of the season is still the case, with the surgeon estimating something in the region of three to four months being the likely time-frame.
"But one thing I will say is that Robert always gives it the absolute maximum when he is in rehab, so we will just have to see how things go in the weeks ahead."