Everton midfielder Ross Barkley needs more 'consistency' under Ronald Koeman, according to former Toffee Leon Osman.
Barkley, 22, has played in all seven of Everton's league games this season, managing one goal and one assist.
But he was left out of the England squad by former boss Sam Allardyce for the match with Slovakia in October.
"Koeman, the way he is around the club, he won't stand for inconsistency and will make him a better player," Osman told BBC Radio 5 live.
Koeman, who succeeded Roberto Martinez at Goodison Park in the summer, told Barkley to "look at yourself" following his most recent international omission.
"I think he's found the transition of new managers tough," added Osman, 35.
"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."
Barkley has 22 caps for his country and has scored more Premier League goals - 17 - than former Liverpool midfielder Steven Gerrard had by the same age.
He has also contributed more assists than Chelsea legend Frank Lampard had by the age of 22.
But he has not played a minute in any of England's last eight matches, last appearing in a friendly win over Australia in May.
Osman, who is now a free agent, added: "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."
Everton sit fifth in the Premier League and travel to leaders Manchester City on Saturday.