The Netherlands international sustained an Achilles injury in Milan's 4-2 Serie A win over Torino on December 9 last year, and has since been out of action.
However, De Jong is slowly approaching his comeback as he trained outdoors for the first time since sustaining the problem on Friday.
"Nigel de Jong did some running at the Milanello sports centre for the first time in four months. His team-mates gave him a round of applause," a statement on the Milan website reads.
The 28-year-old joined Massimiliano Allegri's side from Manchester City at the start of the 2012-13 campaign and has so far made 16 appearances for the Rossoneri in all competitions.
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