The Japan midfielder suffered a suspected ankle injury in the win at Sunderland in midweek.
After last night's FA Cup win against Brighton, Slot said: "There is definitely a chance, but he will be out for a while. We cannot say exactly how long yet.
"That is sometimes different with every injury. Sometimes you can make that diagnosis straight away, sometimes you need a few more days to see how things develop and that last thing is with Wata.
"He will not be in the squad next week and he will not be in the squad the next month, but we're hoping towards the end of the season he has a chance to be there with us again.
"That also depends on the upcoming days where that will lead to.
