The Bob Willis Trophy match between Northants and Gloucestershire in Bristol was called off on the opening day on Sunday after the result was confirmed.
Gloucestershire had reached 6-66 at lunch, but the players did not return to the field after the break and the match was officially abandoned.
The unnamed player was not part of Northamptonshire’s group in Bristol and had been self-isolating at home while awaiting his test result.
However, members of the Northants squad had been in contact with the player in the 48 hours before he started displaying COVID-19 symptoms.
“Gloucestershire, Northamptonshire and the ECB are unified in the belief that player welfare is paramount and that no risks should be taken with the health and safety of the players, officials and administrators involved in this match,” a statement from Northamptonshire confirmed.
“The match has now been abandoned and the Northamptonshire squad will return home to Northamptonshire today.”
It is the first county match to be abandoned due to the ongoing pandemic.
The two counties are due to meet in the T20 Blast on Friday, with the England and Wales Cricket Board to determine a course of action in the coming days.
While the Australia and England players contesting the current T20 International series in Southampton are living and playing inside a strict bio-secure bubble, the same restrictions do not apply to England’s domestic cricketers.
Players are instead asked to adhere to various protocols aimed at limiting their risk of catching the virus.