Kenneth Omeruo has rejected a new contract offer at Chelsea.
The Nigeria defender has spent the season on-loan at Middlesbrough.
His representative, Chika Akujobi, has been quoted as saying he wants a better deal offered from Chelsea before he leaves for the World Cup in Brazil with Nigeria.
"We want them to double the offer, but they said they have a new policy for young players who have yet to break into their first-team and this ensures they do not go overboard with their offers," he said.
"But Kenneth has already proved himself in the English Championship which is even more forceful and physical than the English Premier League, which is more about tactics.
"Chelsea have to come up and they have to do so soon, before the club go on summer holidays."