Footage posted on social media appears to show a security guard mopping the floor where a homeless man was sitting.
The video was taken on Victoria Street in London on Saturday night – and shows the man trying to move his sleeping bag and duvet away from the water as it seeped underneath.
He was heard saying “leave me alone” as his belongings were kicked out of the way.
Another security guard attempted to stop someone from filming, and bystanders could be heard describing the situation as “outrageous” and “bang out of order”.
The homeless man had been sitting outside a Nationwide bank branch – next door to the McDonald’s where the security guards were working.
Damon Evans, who posted the footage on X, tagged McDonald’s and asked: “Do you think it is acceptable for your staff to soak the sleeping bags of homeless people in the middle of winter (or any other time of the year)?
“Disgusting behaviour. He wasn’t even outside your premises.”
McDonald’s UK replied to the footage, and said: “Thank you for bringing this to our attention. It is not one of our employees but a third-party security guard.”
They have also requested more information about the incident so it can be raised urgently with the security guard’s employer.