The summer signing featured for Palace U21s in the win against Premier League U21 opponents Anderlecht.
Riad managed 45 minutes on the night.
Glasner said: “It's a little bit similar to Adam (Wharton) – he had a little bit of reaction after that game, it looks not that serious, but we had to reduce the impact on his knee, and it's something you don't want to have, but something we also know that it can happen, especially when you're out for three and a half months.
“Now we have to find the right doses, and this is how he is, but he will get all our support to be back as soon as possible.”
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