The on-loan Liverpool player tore a medial knee ligament in training during Stoke’s warm weather break in Dubai this week.
Morocco international Assaidi has impressed for the Potters this season, scoring four goals, including the winner against Chelsea in December.
He will stay with Stoke for treatment instead of returning to Liverpool, and manager Mark Hughes said: “It was our only negative from the trip away.
“Unfortunately he’s torn his knee ligament and he’s going to be out, so they tell me, for between four and six weeks.
“That’s a real blow because he was looking really sharp and having a real effect on games for us. But given the medical cover that we have here and the quality of the staff, I’m sure he’ll be back sooner rather than later.”
Andy Carroll is one of three players who could return for West Ham in Monday's crucial home clash against Stoke City.
Newcastle United are reportedly ready to start negotiations about making Kenedy's loan move from Chelsea into a permanent deal.
Michy Batshuayi could be facing a lengthy spell on the sidelines after picking up an ankle injury while playing for Borussia Dortmund.
Max Allegri says he is happy at Juventus and has dismissed suggestions he could be leaving the Italian giants this summer.
Ousmane Dembele has pledged his future to Barcelona and says he will not be leaving the Nou Camp in the summer.
Everton hero Tim Cahill believes his former club are 'confused' and have lost their 'identity' as the Toffees fans grow restless.
Ousmane Dembele has shot down rumours linking him with a shock move to Arsenal and says he will not be leaving Barcelona this summer.
Liverpool striker Mohamed Salah says claiming the golden boot is in his mind but winning the Champions League is far more important.