The Belgium international is said to figure prominently on the Blues’ transfer wish list, as they look to bring added steel into their midfield.
Nainggolan has so far batted away the rumours, joking that the climate in England is not to his liking.
Manolas, though, concedes that the 28-year-old will have to start listening to Europe’s top clubs if he is to grace the very highest level and prove himself to be among the world’s best.
He told Mediaset Premium: “Nainggolan doesn’t like the rain, but he is among the best midfielders in the world and has to get accustomed to that too if he wants to play in the best teams. He can do it, because he’s a phenomenon.
Manolas is also generating plenty of speculation ahead of the summer window, with the Greek defender tipped to soon be heading out of the Italian capital.
He added: “My future is in Roma’s hands. If they want to keep me, they know what to do. If they want to sell me, then I can’t do anything about that.
“It’s difficult to say we’re targeting the Scudetto, because Juventus are really strong and, as we’ve seen, they don’t drop points.
“Our objective is to get into the Champions League and we’ve got a very important Coppa Italia semi-final against Lazio coming up. We can overturn that 2-0 first leg defeat, as we are the stronger side and we just have to prove it on the pitch.”