The 24-year-old French-Ivorian has scored 21 goals in 36 appearances for Lille this season, and has attracted attention from several clubs around Europe as a result.
Closer to home, Manchester United appear to be Liverpool’s main rivals for Pepe’s signature, with Castle’s stating that the striker would be a preferable addition to the squad than Matthijs de Ligt.
“They have made an enquiry with Lille’s forward Nicolas Pepe,” he told The Transfer Window.
“As yet, I’m told, there’s not an offer into Lille for the player. But that to me is a much better addition to Liverpool than De Ligt at present.
“I think they need a creative midfielder, so spend your money there.
“They have to assign a backup left-back and they could probably do with some kind of backup to [Trent] Alexander-Arnold at right-back, unless they want to shift [Joe] Gomez between centre-back and right-back when necessary as they did in this past season.”
Castles added: “I think it’s the creativity in midfield [they need], they lack real quality passing there and invention there.
“And they have been very clever this season in adding set-piece effectiveness to their team. They’ve worked on their set-pieces and they score more goals from them and that’s one way of breaking down opponents that sit in.
“But they still have problems. That’s not solved it for them every time.”