The 27-year-old is being held after a gun and ammunition were found during a search in Newtownards.
The victim suffers a serious head injury after being kicked and punched by two men in Newtownards.
A car was set alight and a house attacked in Newtownards, County Down, in the early hours of Sunday morning.
The discovery of cannabis and cocaine follows searches of businesses in Newtownards on Monday.
The Upper Newtownards Road in east Belfast is closed following the incident.