Beckham's leg is expected to be in a cast for three to four weeks and in a support for a similar length of time but he has already started to use crutches.
Despite the injury, he will remain a Milan player until the end of June, the date at which his loan period expires.
A statement from the club said: "The rehabilitation plan has been established and will start immediately.
"For the first two weeks, the footballer must not put pressure on the injured limb and then he will do so progressively and partially for six weeks before doing specific therapy in the swimming pool.
"The plan foresees a complete recovery in six months, after which he will be able to play again."
Such a timeframe confirms that Beckham will not be fit in time to play in this summer's World Cup in South Africa, which is set to start on 11 June.
Beckham's doctor on surgery
Former Manchester United star Beckham, England's most capped outfield player with 115 appearances, had been bidding to become the first England player to feature in four successive World Cup finals. He shares the record of three with Bobby Moore and Peter Shilton.
The former England captain, who is in his second loan stint with AC Milan from his Major League Soccer club, was injured in the 87th minute of Milan's 1-0 win over Chievo.
Beckham was unchallenged when he suffered the problem and limped off before being carried away on a stretcher.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.