Athletic Bilbao boss Marcelo Bielsa has admitted that he erred in taking off Ander Herrera during the second half of Thursday night's Europa League semi-final first-leg defeat by Sporting Lisbon.
The Argentine coach withdrew the midfielder with just over 17 minutes remaining and the Basques a goal to the good thanks to Jon Aurtenetxe.
Just over 60 seconds later, Emiliano Insua headed Sporting level before Diego Capel then popped up with the winner, leaving Bielsa regretting his decision to replace Herrera with Mikel San Jose.
"The team suffered in the absence of Herrera," the former Chile boss told reporters after the game. "I thought we would win more balls while they were attacking because they were just going forward at that stage.
"We obviously have to win at home now, but that should not be viewed as an unachievable objective."
Athletic had gone into the game as clear favourites in light of their exploits against Manchester United and Schalke in the earlier rounds. However, Bielsa insisted that his players had not been guilty of complacency.
"If there is one conclusion that it is simply impossible to draw after this game tonight, it is that Athletic underestimated their opponents," he argued.
Athletic and Sporting will meet again at San Mames next Thursday, with the game set to get underway at 21.05CET.