The tourist hotspot was cordoned off by police following the incident on Saturday (May 10) at 4.09pm.
The man in his 40s was found with a head injury as he was treated at the scene by medics who arrived in less than a minute.
He was then taken to hospital, where his injuries were found to be non-life threatening.
A man in his 30s was arrested on suspicion of grievous bodily harm.
Officers blocked off a section of the square as bystanders watched medics looking after the injured man.
A Metropolitan Police spokesperson said: “Officers were called at 4.09pm to reports of an altercation in Leicester Square.
“A man in his 40s was treated at the scene by the London Ambulance Service and taken to hospital, his injuries are non-life threatening.
“One man in his 30s has been arrested on suspicion of GBH and remains in custody.”
