The former England captain injured himself in the closing minutes of the match Sunday. Club physician Jean Pierre Meersseman told Italy's Sky TV that Beckham will fly to Finland on Monday for surgery, where he will be treated by specialist surgeon Sakari Orava.
Beckham was on his second loan stint at Milan from Los Angeles Galaxy as he looked to boost his chances of making England coach Fabio Capello's World Cup squad, but the injury is likely to have brought an end to his international career.
The 34-year-old was already becoming an increasingly peripheral player in the squad, largely used as an impact substitute in recent matches.
The injury occurred when Beckham was by himself with the ball at his feet. He shifted his weight and immediately realized there was a problem, reaching his hand down to his left heel.
Visibly in pain and in tears, Beckham went to the sideline for medical attention, leaving Milan with 10 men since all three substitutes had already been used.
"He felt the muscle begin to come up, which is a typical symptom when you break an Achilles' tendon," Milan coach Leonardo told Sky. "This is a real blow."
Sky reported that Beckham said, 'It's broken, it's broken," when he came off.
"He's in a lot of pain," said midfielder Clarence Seedorf, who scored the winning goal after Beckham hobbled off. "This is really bad."
Returning to the starting lineup after Milan's 4-0 Champions League loss to Manchester United, Beckham was also treated for a deep cut to his right cheek following a collision early in the first half.
With the game still 0-0, Beckham nearly scored in the 84th, but Chievo goalkeeper Stefano Sorrentino stopped his close-range effort.
"He was in tears. He didn't say very much," teammate Ignazio Abate said after the game.
With 115 appearances, Beckham holds the record number of caps for England as an outfield player. "He'll probably be out for five or six months," Milan vice president Adriano Galliani told Sky.
"I saw him really suffering. In the changing room I hugged him and told him that if he wants he can join us next year, too.
"He came to Milan to be called up by Capello. Unfortunately that's football. He's got a great strength of soul."
