The 40-year old was walking on a cycle path from Plains to Caldercruix, North Lanarkshire, when he was approached by the shaven-headed man and his black-clad passenger on the quad bike, and a third man wearing a hoodie and riding a dirt bike.
They assaulted and robbed the man before making off in the direction of Plains between 9.30pm and 10pm on Thursday.
The victim made his way to a friend's house nearby and called the police, and he was taken to Monklands Hospital for treatment to a head injury.
The skinhead was aged between 25 and 30 wearing a dark black or purple jumper and trainers, and his passenger was wearing all black.
The man on the dirt bike was slim, about 5ft 11in tall and aged between 20 and 25, wearing a navy hooded top and trainers.
Detective Sergeant John Magilton is appealing to the local community for assistance.
He said: "This was a very nasty incident which left the victim with a head injury, which required medical attention.
"During our enquiries, we have learned that there were several members of the public on the cycle track just before and after the robbery took place.
"The weather was very nice that evening, and it is possible that people may have inadvertently witnessed the suspects in the local area that night, especially as the vehicles they were on would have caused a particular noise nuisance.
"I would urge anyone with information to contact myself and my colleagues at Coatbridge CID on 101.
"Alternatively, please contact Crimestoppers on 0800 555 111 where information can be passed in confidence."