Spain defender Dani Carvajal spoke out in favour of his side's interim coach Fernando Hierro's abilities as a tactician whilst admitting the 2010 world champions have failed to meet expectations at the World Cup so far.
Hierro, a last-minute replacement after Julen Lopetegui was sacked, had his capacity for coaching called into question by former Real Madrid manager Bernd Schuster after the national team scraped their way to the top of Group B with five points by beating Iran 1-0 and drawing with Portugal and Morocco.
Their reward for winning the group is a last 16 clash with tournament hosts Russia on Sunday.
"The first problem Spain have is that Hierro is not a coach, he doesn't have the experience for this level, being a player is not the same as being a coach," Schuster told radio station Onda Cero on Wednesday.
"He came in very late and it's not his fault but it's very difficult for him to take decisions. The team had been built by another person and he's not making the right changes, he doesn't have a plan, he doesn't know how to react."
Carvajal hit back at Schuster in a news conference on Thursday as he defended Hierro, who only has one year's coaching experience, a disappointing season with Real Oviedo in Spain's second tier.
"I think he is more than capable, so I have to disagree with Schuster's words," Carvajal said.
"In the end we are the ones who see him every day and we believe he is qualified to lead the national team. He is a great coach and we'll stand by him until death."
Carvajal said no-one in the team had been happy with their displays so far in the tournament but also claimed the overall level of football in the World Cup has not been high.
"It's obvious we need to take a look at ourselves, we all have to give a little more," he said.
"Here any opponent can cause you trouble. We've received a lot of criticism, but what counts is that we haven't lost a game for two years and we won our group. Few teams have done that. No-one is saying that the play (at the finals) has been good, and neither are we."
Carvajal also warned of the threat that Russia will pose and said it was paramount his side corrected the mistakes they made in their chaotic 2-2 draw with Morocco in their last outing.
"I think if we iron out those errors at the back we'll be very strong," he added. "On Sunday we have a very difficult game against the hosts, who scored eight goals in the first two games and who will have the whole country behind them."