The bouncer throws a right handed punch which leaves a man crumpled on the ground in the clip widely shared on social media.
A police statement said: “We are aware of footage circulating on social media showing an incident involving security staff and a member of the public outside Boxpark in Wembley.
“An investigation into the circumstances, including to establish the identity and welfare of those involved, is under way.
“There have been no arrests and enquiries are ongoing.”
Boxpark said: “Out team are aware of the footage being shared online. This incident is part of an ongoing police investigation.”
A Boxpark employee said: “Julius is a lovely guy. He was here when I did my first shift he was so helpful he showed me around and was just so kind.
“He was just doing his job protecting Boxpark and staff.”
Francis, 57, was a successful boxer throughout the 1990s and 2000s and won 23 of the 48 bouts he competed in.
He competed against a number of boxing legends including Vitali Klitschko in 1998 and Mike Tyson in January 2000.
Francis was knocked down by Tyson just a minute into the second round.
He would win just two more fights after his match with the American heavyweight legend, going on to lose 14 in a row before hanging up his gloves in 2006.
Francis went on to start a fitness company and worked as a security guard.
In 2009, he admitted criminal damage and common assault after punching a car window and spraying a driver with glass – causing minor injuries to his face.
He was ordered to carry out 140 hours of unpaid work and told to pay £200 compensation to the victim, NewsShopper reported.
Francis admitted it was “very stupid of me” at Bromley Magistrates’ Court, adding: “I shouldn’t have done what I did.”