The England international was forced off injured in the second half of Liverpool's Champions League last 16 defeat to PSG on Tuesday night, with Slot saying afterwards it would be a "surprise" if the right-back was fit to play on Sunday.
Slot also faces an anxious wait on Ibrahima Konate, who limped off late on against PSG. Liverpool's boss is hoping the centre-half was just fatigued rather than injured.
“I have to ask but for me Ibou was more that he was tired than it was an injury. With Trent, he had to come off. That’s never a good sign,” said Slot.
“And from what I heard from people that saw the images or how he got injured, that didn’t look very good. So I would be surprised if he is available for Sunday.”
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It was a bruising night for Liverpool, who were knocked out of Europe on penalties after a gruelling 120 minutes.
Slot said he was "shocked" after the defeat but believes the cup final on Sunday is the perfect game to sharpen Liverpool minds and help the players get over their European heartbreak.
He said: “It is maybe not the moment to tell them now but two seasons ago we went out to Real (Madrid) after losing 5-2 at home so if you have to go out, go out the way we did against one of the best teams in Europe and making such a fight.
“I hope every fan around the world was hoping this game wouldn’t stop because it was incredible.
“Two teams had an incredible level and intensity in the first 25 minutes. I also remember the first 25 against Manchester City and Real Madrid but this was unbelievable what we showed in the first 25.
“Over 90 minutes I don’t think we deserved to lose, over 180 maybe it was deserved we went to extra time.
“In extra time I thought maybe PSG was better than us. Then it comes down to penalties and they scored four.
"The good thing is we play a final on Sunday, so mentally that’s probably the best you can ask for, because this is what we are playing football for: to play finals.
“And then there are two-and-a-half weeks in between before we start the season again.
“And if we can play nine times with this intensity – and the ones we play at home with the same intensity from the fans as well – then I am really looking forward to the end of the season.”