Newcastle winger Allan Saint-Maximin and captain Jamaal Lascelles are both suffering from the long-term effects of coronavirus and it is not known when they will return.
The pair were among several players to have contracted the virus when an outbreak hit the club earlier this month.
That forced the postponement of Newcastle’s game against Aston Villa and the training ground was closed for over a week.
Manager Steve Bruce said on Friday that two of his players had suffered “damaging effects” of the virus and had been “struggling for a while with it”.
At that point, the club had not named the players in question.
But after reports emerged on Monday that the players had fallen out with Bruce, the club clarified the reason for their recent absence.
Bruce takes his side to Brentford on Tuesday night in the quarter-final of the Carabao Cup.