Valencia – who have seen the likes of Roberto Soldado, David Albelda and Tino Costa leave the club in the close-season – were humbled by Espanyol last week as they suffered disappointment on their first away trip of the new La Liga season.
A 3-1 defeat meant that Miroslav Djukic's side slipped to 10th in the table, as they failed to follow up their opening-day win over Malaga, despite taking an early lead through new signing Helder Postiga.
Costa was quick to admit that the performance was unacceptable, revealing that he was "ashamed" by the result.
And the Portuguese – who scored the only goal in the win over Malaga – has demanded an improvement for the visit of the champions on Sunday.
Costa told AS: "We really paid attention to (coach Miroslav) Djukic after the match.
"And it was the right time to do so. We feel ashamed of the game we played at Cornella-El Prat.
"We have to improve, work harder and raise our game against Barca. We will have to be perfect to beat them."
