Jose Mourinho has hit back at Barcelona midfielder Fermin Lopez following his criticism of Real Madrid's repeated complaints about refereeing decisions, adding another layer of tension ahead of Sunday's El Clasico at Camp Nou.

The Real Madrid manager was questioned about the controversy during Saturday's pre-match press conference, after Fermin expressed frustration with the Spanish capital club's public statements concerning referees and the ongoing debate surrounding the Negreira case.

Barcelona have made a perfect start to their La Liga title defence, winning all nine matches and establishing a six-point advantage over their fiercest rivals.

However, their impressive domestic form has not prevented another exchange of words between the two clubs before one of the most eagerly anticipated fixtures of the season.

Speaking to Spanish broadcaster Teledeporte, Fermin insisted that Barcelona's performances on the pitch should receive greater attention than the controversies surrounding officiating.

Mourinho responded with a pointed remark of his own, suggesting that Madrid also had reasons to feel frustrated.

"What can I say? There are many things that keep happening that tire us, and Fermin gets tired of our discourse. That's how it is," the Portuguese coach said.

The comments revive memories of Mourinho's first spell at Real Madrid between 2010 and 2013, when disagreements over refereeing regularly intensified an already fierce rivalry with Barcelona.

Mourinho responds to Fermin's criticism of Real Madrid

Fermin's comments came during an interview with Teledeporte, in which the Barcelona midfielder was asked about Madrid's continued references to refereeing controversies.

The Spain international suggested that the subject had become tiresome, particularly while Barcelona were demonstrating their quality through results and performances.

"It's getting a bit tiresome because we're showing our level on the pitch," Fermin explained.

He added that Barcelona's players preferred to concentrate on their own football rather than become involved in disputes surrounding the officials.

The midfielder also suggested that raising such issues suited Madrid's interests, although he did not elaborate on any specific incident.

Mourinho was subsequently invited to respond during his press conference on Saturday.

Rather than enter into a detailed discussion of Fermin's criticism, the former Chelsea and Manchester United manager delivered a characteristically sharp answer.

"There are many things that keep happening that tire us, and Fermin gets tired of our discourse," Mourinho replied.

His response stopped short of identifying exactly which events he considered frustrating, leaving the remark open to interpretation without making a specific new allegation.

Mourinho also addressed questions about the referee appointed to Sunday's fixture, insisting that he did not approach matches with concerns about individual officials.

"I always start from the assumption that the referee is good," he explained, while expressing concern about situations in which established rules are not followed.

The Portuguese manager nevertheless sought to keep attention on the football itself, acknowledging the quality of Hansi Flick's Barcelona side.

He also dismissed suggestions that Barcelona's recent 4-2 Champions League defeat to Paris Saint-Germain would necessarily influence the outcome of Sunday's encounter.

"We arrive in good form. We win matches, play well and score goals, but in Clasicos, it has no influence," Mourinho said.

"These are different matches, and what you have done before doesn't have much significance."

Fermin identifies Mbappe and Courtois as Barcelona's biggest threats

Despite his criticism of Madrid's public comments, Fermin showed considerable respect for two of Mourinho's most influential players.

Asked which opponents he would prefer to remove from Real Madrid's starting lineup, the 23-year-old singled out Kylian Mbappe and Thibaut Courtois.

"Courtois wins them a lot of points, makes a lot of saves, and Mbappe is a special player, so if I could, I'd take them both out," Fermin told Teledeporte.

"But Real Madrid have very good players, and we have to control all of them as a team."

The midfielder's choices reflect two contrasting challenges awaiting Barcelona.

Courtois remains capable of frustrating opponents even when Madrid are under sustained pressure, while Mbappe's pace and finishing ability make him particularly dangerous against teams defending with a high line.

That second threat could prove significant given Barcelona's recent defensive difficulties against PSG, who repeatedly exploited space behind Flick's backline during their 4-2 Champions League victory.

Mourinho, however, was equally respectful when asked about Barcelona winger Lamine Yamal, insisting that Madrid would not abandon their tactical identity simply to contain one opponent.

"He's a great player, and great players deserve respect," the Portuguese coach said, before adding that respecting an opponent did not mean changing an entire team's structure.

Fermin also refused to describe Barcelona as favourites, despite their perfect league record and commanding position at the top of La Liga.

"It's a match either team can win. There are no favourites," he explained.

"We're two great teams, and we have to focus on playing our game, controlling our emotions and the small details."

Victory for Flick's team would extend their lead over Mourinho's side to nine points after only 10 rounds, although the Madrid manager insisted that previous results would count for little once the match begins.

The latest exchange between Mourinho and Fermin has added to the build-up, but both clubs now face the task of settling their differences on the pitch.

Barcelona host Real Madrid at Camp Nou on Sunday, October 25, with kick-off scheduled for 8pm UK time.