Todd Casey said he walked out of the Andersons Bay Rd branch of the fast food chain yesterday afternoon when he was spotted by a group of people in a white van.
As he walked towards his car, the van sped through the car park before stopping behind Mr Casey's vehicle, blocking his exit.
Mr Casey said after he got into his car, a man rushed out of the van wielding a pocket knife, opened the driver's side door and stabbed him in the arm.
The group in the van then fled the scene.
Mr Casey sustained a 1cm cut and was treated by ambulance officers at the scene, who administered a bandage just above his wrist.
He had recently swapped a vehicle with one of the van's occupants after arranging a deal via social media, he said.
The day after the swap, the other party alleged he had supplied a vehicle with a faulty fuel pump, a claim Mr Casey rejected.
''The fuel pump was going good.''
Mr Casey said his future assailant wanted money, but he was not prepared to pay up.
He described one of the people in the van as having a ''beard and a nose piercing'', while a witness said another was ''a ginger''.
A police spokeswoman confirmed the victim and offender were known to each other.
The people in the van, including the assailant, were still at large as of last night.
