The 18-year-old’s promising debut was cut short after 81 minutes when he landed awkwardly following a challenge near the touchline.
He will now be evaluated by the club’s medical staff to determine the extent of the injury.
"Of course, he is down because for him it didn’t feel good immediately, but this is something now we have to assess,” Slot told the media.
"Normally these things don’t happen in five to 10 minutes and you have to wait for tomorrow to see how he comes in and then maybe do an MRI scan to know more about how serious it is.
"Normally the emotions of a player tell you a lot. I saw during the weekend a player in the Dutch Eredivisie who went out completely in tears - Ruben van Bommel, by the way, of PSV - and a day later it proved to be that it was right. Let’s hope for the best."