The France international sat out the goalless draw with West Ham last weekend but manager Alan Pardew hoped he could be back in time for the crunch encounter with QPR on Sunday.
The powerful midfielder has been a key asset for the Toon since joining from Toulouse in January and will be sorely missed if the reports about his health are accurate.
Sissoko has been unable to train this week ahead of the game with the already relegated R's and Pardew is now planning for the last two matches against the Hoops and Arsenal without Sissoko in the reckoning.
The news regarding Sissoko could force the Newcastle boss to push forward his plans to play Hatem Ben Arfa at Loftus Road this Sunday.
Pardew revealed on Tuesday Ben Arfa is struggling with a hamstring injury but is being forced to throw him into service given the club's fight against relegation.