Breandan Rodgers worked with the player whej he was at Chelsea so knos the potential the lad has. Bertrand was on loan last season at Norwich.
"He's a big talent," Rodgers told the club's official website. "He's a boy who has obviously been groomed to fill in for Ashley Cole in the future.
"I was involved in Ryan coming into Chelsea when we took him from Gillingham at 16. And I have worked closely with him for three years or so and nurtured his development. And he's developed into a top-class young player.
"If supporters need to know what he's like, he's very much the Ashley Cole type. Great going forward, very good on the ball, quick and aggressive in defence.
"The modern day full-back, especially in an offensive team. If you look at the Patrice Evras and the Ashley Coles and people like that then those are the mark of the top players in the modern game. And Ryan has the potential to be the same."