Giant defender Jeremy Mathieu emerged from the football shadows four months ago to get a star billing in the heart of the Barcelona defence but it has been a battle since to win over some of the faithful at the Spanish giants.

Mathieu, who will be 31 on Wednesday, was not a regular in the French national side, and had played only a handful of Champions League games for his Valencia club.

The 1.90 metre (six feet three inch) Mathieu could never have imagined he would be given the task of containing the likes of Cristiano Ronaldo, Karim Benzema and James Rodriguez in Saturday's Clasico at Real Madrid.

Mathieu told AFP it was a moment of "joy" and "pride" when he learned of his 20 million euro ($25 million) move to Barcelona in July.

A rejuvenated Barcelona are now top of La Liga but Mathieu acknowledged that he has battled to convince some supporters.

"When I arrived, some people criticised my age and the price paid by Barcelona a lot. But it was not my decision. I am trying to prove my worth on the pitch. It is happening little by little, I am winning my place, changing people's opinions," he said.

The player who made his name at the unglamorous French clubs of Sochaux and Toulouse admitted it was a shock when he got the call to the Camp Nou stadium.

"At my age I could only say yes. In my head I was resigned to staying at Valencia. At my age you don't expect Barcelona to come calling," he said. "But if Barcelona come looking for you it is because you have the level."

Mathieu said it was Barcelona coach Luis Enrique who had wanted him to sign and told him "not to worry."

Now he is in a team three points clear at the top of La Liga and heading comfortably towards the Champions League knockout stages. Enrique has demanded and got more from Barcelona's stars and with Luis Suarez about to start for the first time, there could be more to come.

Mathieu said there could be "fireworks" with Suarez, coming back from his World Cup biting ban.

"I think he can do big things. On the pitch, in training, it shows that he wants to do big things. He is hungry and he wants to get started with Barcelona.

"We don't know yet whether he will start the Clasico but (Lionel Messi, Suarez and Neymar) can hit a defence. We will see on the day, but there could be fireworks," Mathieu predicted.

For Mathieu, the Clasico is a dream come true that could help establish his place in the French team for the European Championships in 2016. A defeat would be a blow to his burgeoning reputation.

"With all these stars, it just makes you dream," said the defender. "It is a match you cannot lose because we have a lot of people behind us: a club, a whole city."

Mathieu's Barcelona exploits have brought him back into the French team after a year out of the squad. He now has four caps.

"At my age, this will be my last challenge in the French team," he said.

"I am going to do everything to be at the Euro and feel what it is like at a great competition."

Barcelona has changed his profile, but Mathieu insists his game is the same.

"People look at you more. That has certainly been in my favour. But I am the same player and I will not change on the pitch. It is the coach's choice but I am very happy being in this French side," said the player who has to win over two teams on Saturday.