The Eagles have not played for 10 days after last weekend’s match at Watford was postponed due to the opposition dealing with a Covid-19 outbreak in their squad.
Most Premier League clubs have experienced Covid issues in recent weeks but Palace had managed to avoid such a situation up to now although the 45-year-old was non-committal on who at Selhurst Park has contracted the virus.
He said: “We hope we are going to be OK but when you are looking at the number of cases around (the country), we start to be worried.
“We had a couple of cases in our football club in the last couple of days. We try our best to prevent and avoid a situation but it is worrying because we don’t know how the next couple of days will go.”
Palace were already without James McArthur (hamstring) and Nathan Ferguson, who is working his way back from a long-term injury, for the trip to Spurs.
Any Covid-19 cases in the squad would further hit Vieira’s preparation for a period where the Eagles take on Tottenham on Sunday before they host Norwich two days later while West Ham are set to visit on New Year’s Day.
The former Arsenal captain enjoyed the busy spell over Christmas during as a player but knows the pandemic only exacerbates the situation.
“It is a busy period but it is the festive period and this is part of the country,” Vieira added.
“I used to love playing during this period and we knew it would be a challenge, so we had to prepare ourselves the best way.
“Obviously with the Covid situation, it makes things more difficult and more challenging.”
Managers from the 20 top-flight clubs held a virtual meeting with the Premier League on Thursday with the congested fixture list and the demands on players some of the topics set to be on the agenda.
Tottenham boss Antonio Conte described the online chat as a waste of time and his opposition number agreed.
Vieira admitted: “When you have a meeting like that with 20 managers, it is always difficult to put your ideas or what you really think across.
“When the meeting finished, you try to understand what was the outcome of the meeting and what was the meeting for? I still didn’t understand what was the conclusion from that meeting.”
Even though there is no suggestion Palace have asked for the Boxing Day clash at Spurs to be off, Vieira feels there is confusion over the requirements needed for a game to be postponed.
He said: “It is just about trying to really understand the guidance or the rules about why we play or why we don’t play, or why this team plays and not this team?
“We need to understand more why those games have been cancelled.
“Yes, we understand the Covid situation and some clubs have been hit by the Covid situation, plus injuries, but I think every situation in every club is different.
“I think there is not a clear guidance or rules about why those games have been cancelled and we may need more information about what is going on.”