The striker has spent the last two campaigns out on loan at West Brom and Everton, and has impressed in both spells - scoring 31 Premier League goals in total.
Lukaku has started just one top-flight game for Chelsea since his move from Anderlecht in 2011, and it is unclear whether he has a future at Stamford Bridge.
The 20-year-old's agent Christophe Henrotay believes that will depend on what players the London club bring in during the close-season.
"For the moment, Romelu belongs to Chelsea," Henrotay told footmercato.net.
"He has two years left on his contract. It's going to depend on Chelsea. After that, we'll see together what the best options are if Chelsea decide to let him go.
"That they want to bring in a big-name striker has been well documented. But Chelsea need lots of great strikers. And if there are too many, they'll choose to allow Romelu to leave.
"But if they think there aren't enough forwards, perhaps Romelu will say, 'I'm interested in prolonging the adventure' but it's still too soon."
