Barcelona coach Xavi Hernández said the club have a bright future with or without him in charge after Wednesday's 4-2 Copa del Rey quarterfinal loss to Athletic Club.

Defeat at San Mamés came just 10 days after Barça were beaten 4-1 by Real Madrid in the Spanish Supercopa final, leaving their hopes for silverware this season resting on LaLiga and the Champions League.

However, despite being disappointed with the result, Xavi was proud of the team's youngsters, with teenagers Lamine Yamal, Pau Cubarsí, Hector Fort and Marc Guiu all featuring in Bilbao.

"All coaches at big clubs depend on trophies, but I feel pride at how we competed against a great team until the end, especially the youngsters," Xavi said in his postgame news conference.

"We're playing with kids. The squad is small. This is what I mean when I say we are in construction. I think this is the start of something big. Whether I am here or not, Barça have a big future.

"There is a really good project, not in terms of me as a coach, in terms of a really good generation coming through. Cubarsí, Fort, Lamine, Guiu and many more players ... Fermín López.

"I think it's the start of something big, but we have to work hard and we have to win. It's about winning at Barça."

Barça fought back from Gorka Guruzeta's goal after just 36 seconds -- the third they have conceded inside a minute this season -- to lead at the break thanks to strikes from Robert Lewandowski and Yamal.

Oihan Sancet headed Athletic level in the second half to take the game to extra time, but not before Yamal had missed two big openings to win the tie for Barça.

"I am disappointed not to take the chances at 2-2, but there is nothing to blame the kid for," Xavi added. "He is a kid of 16 who is playing amazingly. He generates [the chances] himself."

Iñaki Williams, who raced back from the African Cup of Nations [AFCON] to play, and his brother, Nico, then both scored in the additional 30 minutes to seal the win for Athletic.

Barça must now focus on LaLiga, where they are eight points behind leaders Girona, and the Champions League, with a last-16 tie upcoming against Napoli in February, increasing the pressure on Xavi to deliver in those competitions.

"If we not competing at the end of the season, then I will have to leave," he said, reiterating a stance he has taken in recent weeks as the criticism has grown.

"But that does not just go for me, it goes for all coaches. This is a big club. This is Barça. I know where I am and the demands that exist. We have to win trophies -- or at least compete for them.

"Tonight we have competed. We have fought hard and given everything, but against a very good team. Athletic deserved it. Congratulations to them, this is football.

"We are going to try and turn things around in LaLiga and go far in the Champions League. But I know how this works, when you lose, the coach is singled out."

Match-winner Williams was not initially expected to be available for this game, but the Ghana international flew back from the Ivory Coast after his country's surprise early elimination from the AFCON on Monday to take his place on the bench.

He came on in the second half and struck the decisive third goal early in extra time, turning home after his first shot hit the inside of the post.

"I didn't imagine that in my wildest dreams," he told reporters. "It all came off perfectly. [On Tuesday], I couldn't even imagine being here after a really big blow with Ghana, let alone playing.

"I have to thank Athletic for all they did to get me back. It was a party from start to finish tonight and the game ended in the best possible way. I think we deserved to win it.

"Everything has gone so quickly. It was a long journey and I didn't even have time to rest, but I wanted to be here. Even if I didn't play, I wanted to be here to help the team.

"These are the nights everyone involved with Athletic wants to be involved in. We dream of winning the Copa."

Athletic go into Friday's semifinal draw with Real Sociedad, Mallorca and either Atlético Madrid or Sevilla, who meet in the final quarterfinal tie on Thursday.

Barça, meanwhile, turn their attention back to LaLiga, with back-to-back home games coming up in the next week against Villarreal and Osasuna.