Palace go into the London derby game off the back of disappointing results against Tottenham Hotspur and Southampton at the start of the new year.
Chelsea, meanwhile, have enjoyed similarly troubled fortunes of late, having won just two of their last 11 games in all competitions.
Vieira expects the form book to have little bearing on events at Stamford Bridge, however, citing the quality that both teams possess – and the need to focus on what Palace can control: their own performance.
He explained: “The mood has been challenging, of course, because of the results that we’ve had, but I’ve seen a group who have been working well this week and waiting for the game to perform the best that we can.
“We are looking at the squad that they [Chelsea] have and we’re looking at the quality of the players that they have. We’re looking at the quality of the manager [Graham Potter] that they have.
“At the moment, yes, they may be in a difficult period, because things are going against them, but that doesn’t take away the quality that they have.
“We, again, have to perform well, and not think at all about the run of games they [Chelsea] are having at the moment.
“We want to focus on ourselves. We want to improve regarding the last games that we played. We want to be more competitive, and more consistent in our performances, to allow ourselves to win games.”
Discussing Palace’s form, Vieira expanded: “I think there’s always two ways of seeing it: it’s about the results, and the results have not been as good as what we wanted; and then there’s going into the details, analysing the games and looking at our performances.
“We’ve had some up and downs, but overall, I think in some of the games, we showed qualities, but again not enough or not consistent enough to win those games.
“I don’t think you can base your approach for the game based on a couple of games – we have to do our homework about the strength and weakness of the opposition team.
“The good thing is that we’ve had a week to prepare for the game, and now it’s important for us to go there and to perform with a strong personality, with a quality and togetherness that will help us to get a result.”