"My biggest worry (with Pietersen) is that he gets a bit far above himself and doesn't keep his feet on the ground.
"He's got to remember who his friends are. If he keeps that in mind, he will be all right. He has as much talent as anyone that has ever played the game," Warne told The Daily Telegraph.
Pietersen was handed England's Test and one-day captaincy after Michael Vaughan made a tearful exit following the team's recent debacle against South Africa.
Warne said England would miss Vaughan's leadership, that won them the 2005 Ashes, when the two teams square up for next year's Ashes.
"Vaughan is crucial for England to regain the Ashes next year because he is such a good captain," Warne said.