The right-back has yet to pen a contract extension on his deal, which expires in the summer.
While there has been news about Virgil Van Dijk and Mohamed Salah possibly renewing, fans are concerned about Alexander-Arnold going to Real Madrid.
"There’s never been anyone like him in world football or at Liverpool," Riise admitted on Amazon Prime.
"He is exceptional. In modern football, you have to be good defensively and offensively, he is exceptionally good going forward with his passing and vision.
"In his programme notes he mentioned he can see something building under Slot and it’s clear it’s going to be a good journey - will it be with Trent long-term or not? These players keep giving different signals, whether they’re going to stay or go.
“Based on what is said there, he will stay because he enjoys the football and Arne Slot has come in and changed him as a player, especially defensively. I think he’s happy, but it’s more about Trent himself and what he wants from his career.
“Does he need something new, or is he happy here. That is the big question.”
He added: “I think he will go.”