Barca still believe in Clasico chances, says Iniesta
The Catalans currently lie in third, four points adrift of Real, having won just one of their last five away games in La Liga.
However, Iniesta believes the Spanish champions showed in their two recent games against Manchester City in the Champions League that they are still capable of beating anyone on their day.
"We have had bad days, like everyone, but no one can think that Madrid will beat us easily," he told a press conference on Thursday.
"It is difficult to think that there are Barca fans that don't believe in us. This team has won the right to believe in it no matter what the situation is."
Barca boss Gerardo Martino will have the luxury of a fully-fit squad to choose from and looks set to name the side that started the home leg against City for just the second time all season.
That means Neymar and Cesc Fabregas will return after being rested for last weekend's 7-0 win over Osasuna with Pedro Rodriguez and Alexis Sanchez, who struck the winner the last time Barca met Real back in October, dropping to the bench.
And Iniesta is urging his teammates to impose themselves on the game rather than being cowed by the atmosphere at the Bernabeu.
"We need to play a perfect game because that is what the opponent will demand of us, but we are capable of doing so.
"More than thinking about them, we need to think about ourselves. We need to be Barca, to be brave. If we are not then it won't go well for us. When things have gone well, it is because we have played like that."
Madrid haven't been beaten in 31 games in all competitions since the two sides met at the Camp Nou.
That run has allowed Carlo Ancelotti's men to overtake Atletico Madrid and Barcelona, whilst also progressing to the Copa del Rey final and the quarter-finals of the Champions League.
However, the Italian stressed they too have to be at their best to all but kill off Barcelona's title chances.
"We are in good form and desperate for the game to come around. We know it will be difficult and against a great team," said Ancelotti.
"Since the game in the first half of the season we have improved a lot. We will need to be at our best, though, as you need to be at 100 percent to beat Barcelona."
Real did suffer a blow in midweek as 21-year-old forward Jese Rodriguez was ruled out for the rest of the season with cruciate ligament damage in his right knee.
That won't affect Ancelotti's starting line-up, though, as the likes of Luka Modric, Angel di Maria, Gareth Bale and Karim Benzema will return to the side after being rested from the start in the 3-1 win over Schalke on Wednesday.
The biggest winners of the weekend could be Atletico as at least one of their title rivals is guaranteed to drop points, whilst they travel to bottom of the table Real Betis.
Diego Simeone's men will go top for a few hours at least should they win at the Benito Villamarin on Sunday before Real and Barca kick-off.
And Ancelotti warned his Real side not to underestimate Atletico's title challenge even if they do see off Barcelona.
"It will be an open game, but I don't think it will decide the league because Atletico are there too. I think the league will be decided in the last game of the season."
Fixtures (all times GMT)
Celta Vigo v Malaga (2000)
Granada v Elche (1500), Espanyol v Levante (1700), Valladolid v Rayo Vallecano (1900), Athletic Bilbao v Getafe (2100)
Osasuna v Sevilla (1100), Real Betis v Atletico Madrid (1600), Valencia v Villarreal (1800), Real Madrid v Barcelona (2000)
Almeria v Real Sociedad (2100)
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