Barkley joined Leeds as a teenager still learning his trade back in 2013.
It is fair to say that the England international did not show his best form at Elland Road, but Warnock believes that the 22-year-old has progressed hugely in recent times.
“That consistency he’s shown [is a sign of his improvement,” Warnock said, in an interview with Everton boss Roberto Martinez.
“I had him on loan at Leeds, and you could never rely on him. You couldn’t give him an opposition player to pick up.
“But when I watch him now he looks a completely different player and I would imagine he will have a real opportunity to stake his claim for an England spot.”
Barkley made just four appearances for Leeds during his temporary spell with the Yorkshire side, with Warnock regularly overlooking him.
The 22-year-old has progressed hugely from that stage of his career now, however, and he has become one of Everton’s most vital players.
Under Roberto Martinez’s stewardship, Barkley has been handed an important role at Goodison Park and he is now required to be one of the Toffees’ most creative influences.
Barkley has scored 11 times and created eight goals in his 32 appearances for Everton in all competitions this season, and looks destined to travel to France with England for Euro 2016.