The 25 year old Morocco international suffered ligament damage during the club's recent training camp in Dubai.
"He got a block tackle in training and just opened up his knee ligaments," boss Mark Hughes told the club website.
"He is going to be out of action for a little while. We obviously hope that he is going to be back sooner rather than later, but it is one that we will just have to wait on unfortunately."
A statement on Stoke's website added that, while Hughes would not put a timescale on Assaidi's absence, "he will be absent for at least a number of weeks".
For breaking stories and all the great banter like us on Facebook: facebook.com/tribalfootball