Aritz Aduriz starred by netting a hat-trick as Bilbao cruised to a 4-0 win over the Catalans on Friday, leaving them on the brink of their first trophy since 1984.
Coach Luis Enrique was frank in his assessment: "Is a comeback possible? This was just the first half. If there's one team that can turn this around it's Barca."
By virtue of the fact that his side have scooped Liga, Champions League, Copa del Rey and UEFA Super Cup titles in 2015, few can doubt the confidence in Enrique's post-match sentiments. After all, it's Barca. They do not do second best these days.
Although the 45-year-old has a duty to preserve his side's morale, and ensuring that they believe that a comeback is possible, the Blaugrana boss must be preparing for second place at this stage of the tie.
Despite fielding the likes of Lionel Messi and Luis Suarez, a tired-looking Barcelona had no reply for what Bilbao threw at them. Enrique cited his team's hectic schedule as a factor in the defeat - and under the circumstances it may be a valid excuse.
On Tuesday, they endured a two-hour classic as Sevilla took them to extra time in their UEFA Super Cup clash in Georgia, before the treble winners ultimately returned home from Eastern Europe with a 5-4 win. There appeared to be a price for the win.
Given that they had already completed a pre-season tour of the United States, it can be of little surprise, then, to see what happened to them three days later when they met Bilbao at San Mames.
Nevertheless, Enrique also heavily rotated his first XI and tonight's clash should see the return of several familiar faces as they look to defy the odds. Few would back against them.
Recent form: WL
Pre-season form: WLLLW
If Athletic Bilbao brought a 'nothing to lose' mentality into the tie then that it is certainly no longer the case. On the brink of their first trophy since 1984, Ernesto Valverde's men now have everything to lose.
Complacency is now the big risk for Bilbao as they look to end a 31-year barren spell, but Valverde was unequivocal in his assertion that the tie is far from over.
Speaking after their famous win on Friday, the Spaniard remarked that his troops still have "plenty of suffering to do" - the words of a man expecting an anxiety-laden 90 minutes at Camp Nou.
Given who their hosts are, few could blame him or any of the Bilbao squad for refusing to get too carried away. Even the fact that no team has recovered from a four-goal first-leg deficit to win the trophy is unlikely to ease Los Leones' worries.
Still, failing to lift the trophy from here would represent a huge upset - even if it is against Barcelona - but Valverde's side can still expect a stern test.
Recent form: W
Pre-season form: WD
Douglas is also unavailable for Barcelona.
Barcelona possible starting lineup: Bravo; Alves, Pique, Mathieu, Mascherano; Busquets, Rafinha, Rakitic; Messi, Suarez, Pedro
Athletic Bilbao possible starting lineup: Iraizoz; De Marcos, Balenziaga, Laporte, Etxeita; San Jose, Benat, Eraso, Susaeta; Aduriz, Sabin Merino
Head To Head
Friday's victory ended the Catalans' four-match winning streak against Bilbao, whose last victory at Camp Nou came way back in 2001. Since then, Los Leones have only won two of the subsequent 34 meetings - not including the 4-0 earlier this week.
However, Barca have only won by four goals or more on one occasion during the same time period.
We say: Barcelona 3-1 Athletic Bilbao
They will certainly not give up without a fight, but surely Enrique's men left themselves too much to do.
As he pointed out, a four-goal win is hardly beyond his troops, but with a three-day rest period separating both legs, Monday comes far too soon for an already-tired Barcelona to produce the full-blooded effort needed to overturn the deficit.