A man in his 50s was assaulted on Wimbledon Common this morning.
Police were called to the scene, near the Windmill Museum, at 6.40am, to reports of a physical attack.
The man was taken to hospital where he was treated for a facial injury.
His injuries are not thought to be life-threatening.
Police said there was no weapon used in the assault.
A man in his 30s has been arrested on suspicion of grievous bodily harm and remains in custody at a south London police station.
Police investigations continue to establish the motive of the attack.