Everton manager Ronald Koeman has admitted that he is unsure about the future of Romelu Lukaku, but insists that he will not worry about the situation until the end of the season.

The 23-year-old is the Premier League's leading scorer this season with 24 goals but turned down the offer of a new club-record contract earlier this year having previously been expected to commit his future to the Toffees.

Reports have suggested that Everton could look to cash in on the Belgian as a result, with a number of top European clubs thought to be interested in the striker, and Koeman admitted that he does not know whether it will be possible to keep him.

"I don't know. We will see what happens at the end of the season. We like to keep the best players but we know that it is difficult. I don't know if it is possible to keep them at the moment," he told reporters.

"Then we have to analyse the team, (to see) what we need to improve for next season. I think we need, offensive-wise, more players who score more goals because the difference between Lukaku and the rest of the players is too big."

Lukaku has been linked with a return former club Chelsea, whom Everton face on Sunday at Goodison Park.