Ross Barkley must work on delivering on a consistent basis if he is to become a key player for Everton and England, says former team-mate Leon Osman.
The 22-year-old has not featured in the last two international squads despite being a regular at Goodison Park this season.
Barkley has started all seven Premier League games under Ronald Koeman, but he has only managed one goal and one assist, a tally not deemed enough by Sam Allardyce and latterly Gareth Southgate.
Osman believes Barkley's troubles stem from the change of manager at Everton during the close-season, but he is confident the midfielder will start to improve once he adapts to Koeman's style.
"I think he's found the transition of new managers tough," Osman told BBC Radio 5live.
"It can be quite difficult if you play one way under a manager for three or four years and then a new one comes in with new ideas.
"Koeman, the way he is around the club, he won't stand for inconsistency and will make him a better player.
"Consistency is decisions. The better decisions you make the more consistent you are.
"If you were designing a Premier League player it wouldn't be far away from Ross Barkley. He has all the attributes in the world."