Lukaku, who is the joint-top scorer in the Premier League with 19 goals alongside Tottenham Hotspur's Harry Kane, has told Everton he will not sign a new deal which would have made him the club's first £100,000-plus-a-week (S$172,000) player.
"But I am not so afraid about his situation because the player has more than two years on his contract".
The Italian-born Dutch agent recently said that there was a '99.99%' chance Belgium global Lukaku would be signing a new contract with Everton, but that has been thrown out the window following the player's non-committal comments about a reported lucrative extension.
Lukaku, who has been in protracted talks over a new deal, spoke out in frustration this week at a perceived lack of ambition and failure to land big-name players. "You get me? Because we always talk about the teams of the 80s and 70s and if you look it was great", Lukaku said. That's a normal ambition.
Barkley is set to come off contract at the end of next season, and Koeman says the club must do everything they can to retain the player.
"Ross is a boy from Everton and what we need to show for him is the best reasons to stay and of course his situation is different because his (contract) is running out next season", added Koeman.
"But it's impossible to do this in one transfer window, and one season". His behaviour, except some quotes in this interview, is what I like in a player. We like to continue and keep the momentum.
"The player has to understand if he does not sign a new contract by one year [left] you need to make a decision for the club so it knows what will happen next year. Last week doesn't count, this is a new game".