The Frenchman has been linked with a move away from St James' Park ever since their relegation to the Championship was confirmed at the end of May, but has so far failed to secure a transfer.
Everton have become the latest club to reportedly hold an interest in the midfielder, although Spanish giants Real Madrid were also thought to be mulling over an offer earlier in the summer.
United are seemingly determined to stick to their asking price of €40million, but the Newcastle Chronicle claims the Magpies are becoming increasingly concerned that Sissoko's uncertain future could be having a negative impact on their Championship campaign.
The newspaper claims that Sissoko's representatives will meet with officials from both Everton and Inter MIlan this week in Paris, with hopes high that a resolution will be found before the close of the transfer window.
But despite their apparent willingness to sell, the club still found time to wish the midfielder a happy birthday on social media platform Twitter, with Sissoko turning 27 on Tuesday.
He received a flood of abusive messages from Newcastle supporters.