Los Leones' boss has conceded that the club has endured a torrid six months and offered little in the way of consolation for fans after his team's 12th league defeat
An early goal from Javier Saviola was enough to earn Los Boquerones three points at the expense of their Basque visitors, who now sit in 15th place in the table.
"We did not start the game well," the 57-year-old Argentine told reporters after the match. "They scored an early goal, but from the end of the first half to the end of the game we had chances.
"Our campaign has been a negative one, but we can explain all the losses. I'd rather not talk about it."
Athletic have won only one of their seven games in 2013, a run which includes a comprehensive 4-0 home defeat by Espanyol, and Bielsa revealed that he opted to drop goalkeeper Gorka Iraizoz in an effort to improve his team's form.
"Iraizoz has been regularly making mistakes," the former Chile trainer added. "I thought it was time for a change.
"I recognise that it was a difficult decision to make, but it's one that I made and thought was right."
Los Leones currently have 26 points from 24 games, keeping them six points away from the relegation zone.