An outbreak of coronavirus cases at Lincoln have forced the Sky Bet League One club to postpone Friday's fixture with MK Dons.
Several of the Imps' players and staff have tested positive for Covid-19 and the club have informed the English Football League that their upcoming game will not be fulfilled.
Lincoln, who were top of the table last month before a run of five defeats in eight games, are also set to visit Charlton on Tuesday in another match which may be in doubt.
An official club statement read: "Lincoln City FC can confirm that a number of players and staff have tested positive for Covid-19.
"Following discussions with Public Health Lincolnshire and the EFL, the decision has been made to close the Soper of Lincoln Elite Performance Centre to protect the health and wellbeing of all of those connected with the club.
"This closure has led to the postponement of our upcoming fixture versus MK Dons in Sky Bet League One. Whilst the club is naturally disappointed in its inability to fulfil the fixture, the primary concern is the safety and wellbeing of its staff, players and opponents.
"News on the rearranged date for the postponed fixture will be communicated in due course and until that point, in the interest of medical privacy, the club will be making no further comment."
The EFL said an investigation will now take place into the circumstances surrounding the outbreak of coronavirus cases at Sincil Bank.
A statement read: "The club informed the EFL that it would be unable to fulfil the fixture following a number of recent positive Covid-19 tests and the requirement for players and staff to self-isolate as per EFL and Government guidance in order to mitigate against the spread of further infections.
"The circumstances surrounding the postponement will now be the subject of an EFL investigation in accordance with EFL regulations. A revised date for the rearranged fixture will be confirmed in due course."
Earlier on Wednesday, the EFL confirmed during last week's testing for Covid-19 there were three positive cases returned from 4,919 tests on players and club staff from all of its 72 clubs.
A twice-weekly coronavirus mandatory testing programme is now in place for all clubs in the Football League, in line with Premier League sides.
The three positive results were from tests undertaken between March 22 and March 28 and 71 out of 72 clubs returned zero positive tests over that period.
