The Argentine admitted that he was impressed by the Portuguese opposition, but bemoaned his own team's lack of stability.
"Academica played a very good game," he said. "They took advantage of the chances we gave them and they won fair and square.
"Unfortunately, we did not play the game we wanted to play. There was no stability in our game."
A Wilson Eduardo brace seal the points for Academica and ended the Spaniards' 16-game unbeaten run in European competition.