Warner, 26, has been dropped for Wednesday’s Champions Trophy match against New Zealand.
Cricket Australia said he was involved in an alleged physical altercation in a bar hours after Saturday’s loss to England at Edgbaston.
The ECB said Warner had apologised for an ‘unprovoked physical attack’.
In a statement, the ECB added: “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.”
“Warner has admitted behaving inappropriately and has since apologised to the player involved who has accepted the apology.”
“ECB has concluded that this is a matter for Cricket Australia and have no further comment to make.”