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 5 live.
"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."