"We can confirm that Ross was the victim of an unprovoked attack by a stranger who approached him on Sunday evening," lawyers acting on Barkley's behalf said in a statement.
A video that circulated on social media showed Barkley having a seemingly friendly conversation with an unidentified man, who then seemed to punch him twice before being restrained by bystanders.
Local police said they were looking into the incident.
"Merseyside Police is aware of footage online reportedly showing an assault in a bar in Liverpool city centre," police said in a statement.
"No report of an assault has been received, but officers are making enquiries to establish the circumstances of the incident."
The member of staff who took the images and then released them has been sacked, the establishment's management tweeted later on Monday.
"Incidents like the one circulating the internet from a recent altercation in the bar are very rare and extremely unwelcome in the venue," read the tweet from the account @santachupitos (the name of the bar).
"There should be no place for this (in) any walk of public life. The incident on the evening was handled quickly and professionally and no injuries occurred.
"We can confirm that we have fully investigated and dismissed the member of staff responsible for illegally recording and leaking imagery."
Everton are yet to comment on the incident, which is said to have occurred hours after Barkley, 23, starred in their 4-2 home win over Leicester City in the Premier League on Sunday.
Everton manager Ronald Koeman warned after the game that Barkley will be sold if he refuses to sign a new contract at the club.