The French winger is wanted by Marseille on loan but won’t be allowed to leave unless Newcastle sign a replacement.
It is also believed that United would prefer a cash only deal for the ex-Velodrome winger.
However, Sissoko, who pledged his short-term future to Newcastle, feels that he should stay on Tyneside and fight for his place.
Sissoko, who appeared on French TV over the weekend, said: “It’s true that since he’s arrived at Newcastle it hasn’t gone very well for him.
“I’m there and I try to give him as much advice as possible. I know it’s not easy but I tell him to hang on and to fight.
“If he has the chance to go to Marseille and to play that would do him good.
“If he stays at Newcastle then try and fight and do everything to change the situation.”
Sissoko also spoke about his own future beyond the summer and said: “There’s the Euros at the end of the season so I’ll try to play in that and afterwards we’ll see what my future holds.”