Kevin Mirallas missed Everton’s defeat at Chelsea due to ‘attitude’ problems.
Images circulating on social media showed Mirallas preparing to board a flight as the Blues prepared for the 2-0 reversal at Stamford Bridge on Sunday.
Olympiakos have been linked with the Belgium winger, who recently signed a new three-year deal, as his Goodison Park prospects appear ominous.
Ronald Koeman confirmed that Mirallas was omitted from the Everton squad that travelled to London as he is unhappy with his place in the club’s plans.
“He was out because he is struggling to deal with moments in the season and was disappointed,” said Koeman.
“Everybody can be disappointed but I expect everybody to be part of the team.
“If somebody is showing that he is disappointed and his attitude is not the same then I have to make a decision.”
Pressed on whether Mirallas could leave Goodison Park before the transfer window closes on August 31, the Dutchman replied: “I don’t know.”
Koeman also paid tribute to Mo Besic’s decision to play in the Stamford Bridge defeat less than 24 hours after his father was shot in his native Bosnia.
He added: “I spoke to him yesterday evening and he’d spoken to his father.
“Today after the game he told me he’d be in contact with his family. I don’t know really what happened, but what came out in the reports is true.
“He said he was ready and committed. After the game he will talk to his family to see what he needs to do.”