Everton manager Ronald Koeman has warned midfielder Ross Barkley that he "needs to improve" after substituting him at half-time in the 3-0 win at Sunderland on Monday.
Barkley -- left out of Sam Allardyce's first England squad -- was withdrawn at the Stadium of Light after losing possession too often, Koeman said at a news conference.
"There was a reason to change Ross at half-time because he did not play well and lost many balls," Koeman said. "Players of that quality can't lose that many balls.
"I had talks with Ross that he needs to improve, but we'll see at the weekend [at home to Middlesbrough].
"We spoke to him and he understands. We showed him the clips, and there's no escape."
Former Southampton manager Koeman said he wanted to see Barkley "be the key player between the defenders and the strikers."
"He's that position in the midfield to create, but also defensively to be part of the team," he added.
"In all aspects he can improve and needs to improve, but he is a young player."
But Koeman said he did not believe Barkley's failure to feature for England at Euro 2016, was behind his loss of form.
"In my opinion that's the past, and what counts now is what happens now," he said.
"You get game time in the national team because you play at a good level with your club and that's deserved game time in the national team."