The injured police constable attached to Kahatagasdigiliya Police station is receiving treatment at Anuradhapura Teaching hospital.
The altercation occurred between the constable and two motor cyclists when the constable flagged them down to stop as one of the motorcyclists was riding without a helmet.
Later, the two returned with another five accomplices, threatened the policeman and demanded that their driving license be returned.
Police said the constable was attacked with a sword as he refused to return the driving license.
The injured policeman was rushed to Kahatagasdigiliya hospital and was transferred to Anuradhaprua Teaching hospital later.
The suspects have been identified as residents of Ranpathwala and Rotapokuna in Kahatagasdigiliya.
Kahatagasdigiliya police said that investigations have been initiated to arrest four other suspects connected to the incident.