Ronald Koeman admits Ross Barkley will be sold this summer if he does not sign a new contract at Everton.
The 23-year-old England midfielder's current deal expires at the end of next season.
Barkley will be of interest to a host of other Premier League clubs and Koeman says Everton must try their best to convince the academy graduate, who has made over 150 appearances for the club, to remain at Goodison Park.
"Ross is a boy from Everton and we need to show him the reasons to stay," said Koeman, who is also battling to persuade Romelu Lukaku to sign a new contract.
"But Barkley's situation is different to Romelu because next season will be the last year of his contract.
"You make decisions at the end of the season and you sign a new contract or you sell the player. There is no 'ultimatum' but that's business - and the player needs to understand this."
Everton are seventh in the Premier League with 10 games remaining and three points behind fifth-placed Arsenal, having played two games more.
Koeman said: "What we want to do and like to do is to show everyone that if there is one club out of the big six to make the next step then its Everton.
"But it's impossible to do this in one transfer window, and one season. It takes time. But this is a message for everybody; the manager and Everton is trying to get the best team it can. But there is competition."