A man has been taken to hospital after being attacked by a dog, believed to be an American XL bully, in a south London park.
The Metropolitan Police said the victim, aged in his 40s, was bitten on the arm shortly after 6pm on Friday.
The owner of the grey XL bully fled the scene after the attack before officers arrived, said the force.
Efforts are now being made to track down the owner.
A spokesman said: “Police were called by London Ambulance Service at 6.07pm on Friday, Sept 22 to Pasley Park after a man, aged in his 40s, was bitten by a dog. He was taken to hospital with injuries to his arm.
“The owner of the dog left the scene with the dog prior to police arrival. The dog is believed to be a grey-coloured XL bully. There have been no arrests. Inquiries are ongoing.”
The mauling is thought to be the latest by the XL bully breed, which is soon to be added to the list of breeds covered by the Dangerous Dogs Act following a spate of attacks.
The dogs have been involved in a number of incidents around the UK, including in London where four-year-old Nehal Islam underwent surgery after an attack at a park in Newham.
Rishi Sunak, the Prime Minister, has said he would ban the breed by the end of the year, as it was clear the incidents were not due to a “handful of badly trained dogs” but part of a “pattern of behaviour”.
However, owners will be allowed to keep registered dogs belonging to the breed if they have them neutered and muzzle them in public.
It comes as hundreds of XL bully owners marched in the capital to protest against plans proposed by the Prime Minister to ban the breed.
Before the event, however, organisers warned protesters not to bring their dogs to the event, claiming “police will antagonise and seize your dog”.
The American XL bully breed, which is not recognised by The Kennel Club, has a reputation for aggression.
Around 70 per cent of dog-related deaths in Britain are thought to be caused by XL bullies.
Half of all American XL bully dogs are descendants of one “killer” inbred pet called Kimbo which has produced dozens of unstable and violent animals, analysis by The Telegraph has found.
A 60-year-old man was arrested earlier this week after Ana Paun, aged 11, was attacked by an XL bully and Staffordshire bull terrier cross in Birmingham in September.
Two men who went to her aid were also injured and needed hospital treatment.
Luna-Ann, a four-year-old, from Nuneaton, Warwickshire, needed 40 stitches and plastic surgery after she was bitten in the face by what her mother believes was an American bulldog crossed with an XL bully at a neighbour’s house in April.