Leyton Orient have confirmed that "a number" of first-team players have tested positive for coronavirus.
The O's are due to host Premier League Tottenham in the Carabao Cup on Tuesday and are in discussions with Public Health England about whether any further action needs to be taken.
The club said in a statement that the tests were carried out after Saturday's 2-2 draw with Mansfield in League Two.
Their most recent opponents - Plymouth, Mansfield and Oldham - have been told.
"Leyton Orient's priority is the health and wellbeing of its players and staff. Those who have tested positive will now strictly follow government self-isolation guidelines," the O's said.
"The Breyer Group Stadium and training ground facilities will be closed until further notice."
It is understood that if Orient are unable to field a team, the game will be awarded to Spurs as there is not enough room in the schedule to rearrange the tie.
Tottenham have a more congested schedule than most because of their Europa League commitments, with their next game in that competition in Macedonia against Shkendija on Thursday.
Orient's tie with Jose Mourinho's men would have seen them potentially come up against striker Harry Kane, who paid to promote charities on the front of their shirts in May. The England captain made his professional debut during a loan spell with the O's when he was 17.
This season, English Football League clubs do not have to do mandatory coronavirus tests on their players and staff.
Orient have been doing medical questionnaires every morning and said they would pay for testing to be done in advance of their cup tie, but Spurs offered to cover the cost.
The EFL say they are "awaiting the outcome" of Orient's discussions with Public Health England.
Plymouth, who were beaten by Orient in the previous round of the EFL Cup, and Mansfield say they will test their players and football staff as a result, adding that none of them currently have symptoms.
BBC Sport's Simon Stone
This news is an escalation of what has been a long-standing worry for all clubs outside the Premier League and Championship.
Clubs have to pay for tests themselves, so Leyton Orient - and Mansfield and Plymouth, who played them recently - are having to absorb an additional cost. It was one of the significant factors behind Leagues One and Two calling an early end to their 2019-20 season.
Now, those same clubs are wondering how they are going to pay the bills having decided to start the new campaign in the belief supporters would be allowed into stadiums, something there is now significant doubt about.
The National League has already said its planned start on 3 October is unlikely to go ahead without supporters but is continuing with pilots at friendlies, which are due to take place this week.
As any business owner knows, uncertainty is the worst position to be in.
For all these 'elite' clubs, the nightmare scenario of having to pay to stage games with no income is suddenly becoming very real.
Without some kind of intervention, this is an unsustainable situation for all but those with owners whose pockets are very deep indeed.