Barcelona have leaked eight goals in their opening two official games of the season and will need a drastic improvement in defence if they are to have any chance of denying Athletic Bilbao the Spanish Super Cup.
After edging Sevilla 5-4 to win the European Super Cup last Tuesday, Barca suffered a 4-0 drubbing at Bilbao in Friday's first leg and host the Basque side for the return on Monday.
The defeat for the Spanish and European champions at the San Mames, when coach Luis Enrique fielded a weakened side, means their hopes of matching 2009's feat of winning all six competitions they contested are hanging by a thread.
Luis Enrique has refused to throw in the towel and told a news conference on Sunday he and the players are "utterly convinced" they can turn the tie around.
If they manage it, they will prevent Bilbao lifting their first silverware since they won the Spanish Super Cup in 1984-85.
"It's a challenge that a team of this quality is capable of meeting," Luis Enrique told reporters.
"If we do things well we will have a chance," said the former Barca and Spain midfielder, noting that his side regularly put four goals or more past opponents.
"We will be fresher than in the first leg and when Barca is playing anything can happen."
Barca's versatile Argentina international Javier Mascherano, who normally plays in central defence but was deployed in midfield for the first leg, said the team had not deserved to lose by such a wide margin.
"In these two key games our opponents have been very effective," he told an earlier news conference.
"We have to improve and minimise the errors but we are not going to go crazy.
"Tomorrow it is vital that they don't score. You are always learning in football and the match the other day gave us a lot to think about for the future."
Barca have little time to set things right before they begin their quest for a sixth La Liga title in eight years at Bilbao on Sunday.
Luis Enrique will have only two of his formidable attacking trio available for Monday's game at the Nou Camp as Neymar has contracted mumps and will again be unable to join Lionel Messi and Luis Suarez up front.
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