Nyoni came into the club's academy from Leicester City a year ago and is already making waves.
He impressed departed boss Jurgen Klopp and will likely get a chance to show Slot his qualities in pre-season or later on in the campaign.
"Trey is fabulous," stated Under-21s coach Barry Lewtas, per Liverpool Echo.
"It's a nice part of the job for me. Trey spent a short time with the U18s and then moved up, and he's been settling into the club this season. You want the boys to hit the ground running straight away when they come in, and Trey did that. To his credit, it shows his mentality and how he approaches the game.
"Hopefully Trey will spend a long time at Liverpool. But he has managed to do the lot he settled quickly, he integrated with the group, the staff and his level of performances were really good. Trey is now familiar and it'll be important he continues on the path he's on."