Cricket Australia (CA) stood down Warner for a breach of code of behaviour. CA said the opener had an alleged physical altercation with an England player (unnamed).
A report in "The Telegraph" newspaper website claimed that Warner "punched" Root after the England batsman had walked into the bar with a fake beard and wig.
"Root was wearing a fake beard and wig in the Walkabout bar on Broad Street in Birmingham. Warner pulled the beard off before punching Root on the chin," the report said.
"Warner was then pulled away by his Australia team-mates and the small group of England players, believed to include Stuart Broad and Chris Woakes, immediately left the bar," it added.
In a statement, England and Wales Cricket Board (ECB) said, "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."
Warner was last month fined by CA for Twitter rant against journalists.