Derby have been forced to shut their training ground at Moor Farm due to a rise in positive coronavirus cases at the club.
Wayne Rooney's side were beaten by Sheffield Wednesday at the weekend, who have since shut their own training ground on Monday.
Now The Rams have confirmed that a number of players and staff from the first-team have gone into self-isolation after testing positive for Covid-19.
A statement on the club's official website said: "Staff members and players were tested on Monday and have subsequently returned a number of positive results.
"The names of those individuals will not be made public for medical confidentiality reasons, but they and their close contacts must now serve a period of isolation at home in line with UK Government guidelines.
"In accordance with Derby County and EFL COVID-19 protocol, the club's Moor Farm training ground has been closed with immediate effect.
"In addition, the club is in dialogue with the EFL and Football Association in relation to upcoming fixtures."
Derby are due to travel to National League North side Chorley on Saturday for their third round clash in the FA Cup, but that fixture could now be in doubt.
If they are not able to name 14 players in their matchday squad, the match would need to be rescheduled prior to the fourth round starting two weeks later.
Under new rules, Derby would otherwise forfeit their place, with Chorley receiving a free pass through instead.
The club are also in ongoing consultation with the EFL regarding their forthcoming league fixtures, the next of which is at home to Rotherham on January 16.
Derby are currently stuck in the relegation zone sitting 22nd in the Championship.
