Porto coach Sergio Conceicao was upset with ref Anthony Taylor after defeat to Barcelona last night.
Barca won their Champions League encounter 1-0 in Oporto thanks to Ferran Torres' winner.
Conceicao later said: "It was a very good game, well above average on our part. We nullified many of Barcelona's strong points and managed to provoke situations in the final third.
"But at the end of this match we have zero points, we have not added anything, and high competition requires high maturity."
At the end of the first half, a bad pass from Romario Bar allowed Torres to intercept and score the only goal of the match.
"In general, I am very proud of the determination and ambition with which we have played and the work we have done, but this is high competition, we have to be focused the entire game and, when we are not like that, we pay dearly for those moments in which that we make unforced errors," Conceicao added.
"We played against more than one club," he concluded in a criticism of the refereeing of Englishman Taylor.