The incident took place in a Birmingham bar in the aftermath of England's 48-run win over Australia at Edgbaston.
Warner was stood down from Wednesday's Champions Trophy match as a result, with the England and Wales Cricket Board confirming that he had "admitted behaving inappropriately and has since apologised to the player involved".
The ECB also stated that their player, who remains officially unnamed, was in no way culpable for the incident and did not retaliate.
Warner has been charged with breaching Rule 6 of Cricket Australia's Code of Behaviour, relating to 'unbecoming behaviour'.
His place on the forthcoming Ashes tour is now in serious doubt and the 26-year-old will be waiting with bated breath over any disciplinary action.
The ECB said: "Following a statement issued this morning by Cricket Australia, the England and Wales Cricket Board confirms that David Warner initiated an unprovoked physical attack on a member of the England team in a Birmingham bar following England's 48-run victory over Australia.
"Warner has admitted behaving inappropriately and has since apologised to the player involved who has accepted the apology.
"Following a full investigation the England team management has concluded that the England player was in no way responsible for nor retaliated to the attack.
"ECB has concluded that this is a matter for Cricket Australia and have no further comment to make."
Details of Warner's indiscretion came to light when CA confirmed the charge against him.
Their statement read: "Cricket Australia advises that Australian batsman David Warner has been stood down from Australia's ICC Champions Trophy match against New Zealand tonight after being reported for breaching the CA Code of Behaviour.
"Warner has been reported for breaching Rule 6: Unbecoming Behaviour after he was allegedly involved in a physical altercation with an England player in the early hours of Sunday morning following the ICC Champions Trophy match between the teams in Birmingham.
"Team management have stood down Warner pending the outcome of the hearing, meaning he will miss Australia's match against New Zealand in Birmingham.
"CA will convene the Code of Behaviour as soon as possible. Details will be provided once the time and date is confirmed.
"CA will not be making any further comment until after the hearing."
The incident continues a difficult time for Warner, who was last month fined A$5,750 (Dh20,077) following an outburst on Twitter.
Warner was given the maximum available fine after he pleaded guilty to breaching rule 6 of the code of conduct over an argument with journalists Robert Craddock and Malcolm Conn.
Warner took exception after his photograph was used alongside an article by Craddock which described the IPL as a "smouldering cesspit" and "the sunniest of places for the shadiest people" before questioning the integrity of the competition in the wake of the latest spot-fixing scandal.
Warner referred to Craddock as a "p***k" on Twitter and said both writers "talk s***".
Warner later apologised for his language and discussed the issue in person with Conn, who had tweeted: "You lose 4-0 in India, don't make a run, and you want to be tickled on the tummy? Win the Ashes and get back to me."
Warner's Twitter conduct this week has been significantly less inflammatory, with the left-hander unexpectedly writing about his fondness for turtles, birds and mountains.
Just on Tuesday, he replied to a fan's question about his favourite part of being a cricketer with the answer 'being able to smile after failing'.
How long that smile remains could depend on the findings of CA's disciplinary officers.
Root, meanwhile, trained with his England teammates at the Kia Oval this morning ahead of Thursday's game against Sri Lanka at the south London venue.
England captain Alastair Cook is expected to address the alleged altercation at his pre-match news conference, which is due to take place around mid-day.
It is understood members of both teams were in the Walkabout Australian theme bar in Broad Street at some point that night.
West Midlands Police said: "We were not called to an incident."
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