Lincoln City's League One games against MK Dons on Friday and Charlton four days later have been postponed because of coronavirus cases in the Imps camp.
The English Football League announced three positive Covid-19 tests from one club in its latest round of testing from 22 to 28 March.
Lincoln have closed their training ground, while players and staff have begun a period of self-isolation.
A new date for the matches will be announced in due course.
The EFL will investigate the circumstances surrounding the postponements.
"Whilst the club is naturally disappointed in its inability to fulfil the fixtures, the primary concern is the safety and wellbeing of its staff, players and opponents," a statement on the Lincoln website said.