The 24-year-old revealed via his Twitter account on Thursday that he had undergone treatment at Clairefontaine, France's training base.
The Frenchman did not reveal the nature of his injury, but confirmed that he will be absent for at least a fortnight, ruling him out of this weekend's visit of Manchester United and a trip to Stoke City the following Saturday.
"Early rehabilitation Clairefontaine today!! Back in 2 or 3 weeks!!" he tweeted.
Sissoko has started all of Newcastle's 32 Premier League games this season, but was substituted 12 minutes from time in Saturday's 4-0 loss at Southampton.
Alan Pardew's side slipped to ninth after that defeat - their second in a row - but that still represents a marked improvement on last season's 16th-place finish.
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