The midfielder was forced midway through the first-half of Liverpool's preseason friendly win against Real Betis in Pittsburgh on Friday.
Afterwards, Slot said: "I think it's too early to tell. He maybe could have played on, but I think maybe you could see he was not at 100 per cent.
"In a friendly game, with so many days coming up in our tour, it was best to take him off. Hopefully he can recover really fast, but we have to wait and see.
"We hope he recovers really fast so we can see him in the next few games."
Slot added: "It's always a pity if he has to go out after 25 minutes, half an hour. And before that you could see that he was not completely free.
"It was unfortunate because he had two really good weeks during the training sessions so I looked forward to seeing him in the game, but unfortunately he had to go out.
"The good thing about that was that we brought someone that impressed me in the 45 minutes to an hour he played afterwards.
"That was the positive thing of Curtis going out for Trey (Nyoni), but of course for Curtis it's a pity that he couldn't play on."