The Rossoneri midfielder is expected to miss the next six months after falling to the ground awkwardly midway through the first half of his side's victory in Turin
The defensive midfielder went down unopposed in an attempt to win the ball back in the 22nd minute, and tests later revealed that he suffered a serious injury.
The news will come as a big blow to the Milanese club, who are seventh in Serie A and trail league leaders Juventus by 14 points.
"AC Milan announce that during the match between Torino and AC Milan, Nigel de Jong sustained a subcutaneous rupture of his left Achilles tendon," read a statement on the club's official website.
"On Tuesday, the player, accompanied by Rossoneri medical staff, will attend an appointment with Professor Orava."
In response to the news that the 28-year-old would miss the remainder of the campaign, his coach Massimiliano Allegri replied: "It's a terrible shame about De Jong, who will be out for the rest of the season, and of course all the lads dedicate the win to him.
"We'll see what to do about De Jong's role in January, but we already have Sulley Muntari, Massimo Ambrosini and Mathieu Flamini."
De Jong joined Milan in the summer from Manchester City for an initial £3.6million and has made 15 appearances for the San Siro outfit, scoring once in the process.