Liverpool closed their training ground on Wednesday after "multiple new" coronavirus cases including a positive test result for assistant manager Pep Lijnders, throwing their League Cup semi-final at Arsenal into further doubt.
Manager Jurgen Klopp and three players -- Alisson Becker, Joel Matip and Roberto Firmino -- were already isolating before the latest wave of infections.
Lijnders, who took charge of the team for Sunday's 2-2 draw at Chelsea, tested positive for Covid-19 late on Tuesday.
The club cancelled Wednesday's pre-match press conference, at which Lijnders was due to speak, a day before the first leg of their semi-final at the Emirates.
Liverpool have other personnel issues, with a number of players including Thiago Alcantara, Takumi Minamino and Divock Origi all absent through injury, while Mohamed Salah, Sadio Mane and Naby Keita are now on Africa Cup of Nations duty.
"Liverpool Football Club can confirm the first-team training facilities at AXA Training Centre have been temporarily closed due to a rapidly growing number of suspected positive Covid-19 cases," the club said in a statement.
"The Reds acted to suspend operations within the facility today after the latest round of testing revealed multiple new suspected positives."
Liverpool said they had lodged an application with the English Football League for the postponement of Thursday’s match in London.