Lukaku, who scored his eighth Premier League goal of the campaign in the Toffees' 4-0 defeat of Stoke on Saturday, said in an interview last week he was keen on staying at Goodison Park for a second campaign.
However, Mourinho has swiftly quashed such a possibility and again questioned the Belgian striker's attitude.
"Maybe there is a new rule in football that when the season finishes every player is able to decide their own future?" Mourinho asked rhetorically at his press conference on Tuesday.
The Portuguese's latest remark about Lukaku comes four days after he called on the 20-year-old to explain why he had made a transfer deadline day loan switch to Everton.
"Romelu likes to speak," Mourinho said on Friday. "He’s a young boy who likes to speak. But the only thing he didn’t say is why he went to Everton on loan. That’s the only thing he never says. And my last contact with him was to tell him exactly that. ‘Why do you never say why you are not here?’"
Lukaku had a penalty saved by Manuel Neuer in Chelsea's European Super Cup shootout defeat to Bayern Munich three days before he agreed to join Everton.
Signed by Chelsea for around £20 million from Anderlecht in 2011, Lukaku has made just 15 appearances for the Blues and spent last season on loan at West Brom, where he scored 17 goals.
He has so far hit more League goals than Chelsea's three main strikers, Fernando Torres, Samuel Eto'o and Demba Ba, this season.
Lukaku is not the only Belgian out on loan from Chelsea. Goalkeeper Thibaut Courtois is into his third successive term with Atlético Madrid and Eden Hazard's brother, Thorgan, is currently playing for Zulte Waregem.
Chelsea travel to Sunderland on Wednesday night while Everton will make the short trip to champions Manchester United.