The Netherlands international arrived from Ajax in the close-season, but has only made two Premier League appearances before being struck down with the problem.
However, the 25-year-old suffered a blow when he sustained the injury back in September.
Newcastle stated the midfielder was likely to be out for "a number of months", but there was some positive news on Tuesday when De Jong took to his Twitter account to reveal he is approaching fitness.
"Finally my boots back on! First session outside," he wrote.
De Jong signed a six-year deal upon his arrival at St James' Park after seven years at Ajax, where he won four consecutive Eredivisie titles.
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