Lukaku moved to Stamford Bridge from Anderlecht three years ago in a reported £20m deal but has spent the last two seasons on loan - firstly at West Brom and latterly Everton, where he has scored 17 goals this term.
There were also reports of a falling-out with Jose Mourinho and Lukaku's agent Christope Henrotay told the Evening Standard: "For the moment, Romelu belongs to Chelsea.
"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."