Newcastle have closed their training ground following an outbreak of coronavirus among players and staff.
The north-east club shut the Benton complex on Monday due to a number of Covid-19 cases, the PA news agency understands.
Boss Steve Bruce revealed after Friday night's 2-0 victory at Crystal Palace that three players had tested positive and were self-isolating.
The squad underwent further testing over the weekend and further individuals returned positive tests.
The first-team players have not trained since the win at Selhurst Park.
Another round of testing is due to take place this week ahead of Friday's match against Aston Villa, which the Magpies could request to postpone if the virus continues to spread.
Premier League rules state that games should proceed as long as teams have a starting line-up plus three substitutes available, which can include players from the development squads.
Speaking after Friday's game, Bruce said: "It has been a tough week.
"We sincerely hope (to avoid an outbreak). It is very difficult at the minute. We have three confirmed players and unfortunately a member of my staff.
"It is a concern and difficult to manage. We are trying our utmost to make sure we try and stay as safe as we can.
"Of course my concern is not just the welfare of the players, which is vitally important, but my members of staff too. We will do our best but it is difficult at the moment."
