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Barkley -- left out of Sam Allardyce's first England squad -- was withdrawn at the Stadium of Light after losing possession too often, Koeman said at a news conference.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].