Ross Barkley is likely to be sold in the next transfer window if the Everton midfielder fails to extend his contract with the Merseyside club, manager Ronald Koeman warned on Thursday.

Barkley, who has been linked with possible transfers to Chelsea or Manchester City, has 18 months remaining on his current deal and British media reports suggest no contract talks are planned until the end of the season.

"Football is a business, you make decisions. He (Barkley) needs to sign a new contract or you sell the player," Koeman told reporters on Thursday.

The 23-year-old, who came through the ranks at Everton, has scored five goals in 29 appearances this season and Koeman stressed that he has not offered an ultimatum to the player.

"I think the player needs to understand this. It's not an ultimatum but I spoke to Ross about a new contract and it's up to the board to get that over the line," Koeman added.

"If not, then the player could see a new future for himself, but that is normal. It's not strange talk."

Earlier this week Romelu Lukaku rejected a new long-term deal from Everton that would have made him the best-paid player in the club's history, according to British media, questioning the seventh-placed Premier League side's ambition.

Koeman said he was far from pleased with Lukaku's comments but would not drop the Belgian striker, who is the league's joint-top scorer with 19 goals so far, for Saturday's match against third-bottom Hull City.

"Of course I am not happy about that interview because if Everton is not a club with a lot of ambition then I'm not the manager," the Dutchman said.

"There is no need to put him out of the team. The team is playing well. Every Premier League game is difficult."

Koeman is still hopeful Lukaku will extend his stay at Goodison Park and is remaining calm regarding the current contract standoff.

"They are still trying to get the contract over the line," he added.

"I'm not so afraid about the situation because the player has two more years of his contract. Everyone knows anything can happen in football but you have to respect your contract."