Napoli coach Rafa Benitez says Yevhen Seleznyov's late goal at the Stadio San Paolo should have been ruled out for offside.
Napoli dominated the first leg of their Europa League semi-final against Dnipro Dnipropetrovsk but had to settle down for a draw after substitute Yevhen Seleznyov scored in the 80th minute.
And the Spaniard says the tie has been compromised by the referee's decision not to disallow the goal.
"This game was affected by an invalid goal, we're angry but we have to look forward to the game in Kiev," Benitez said.
"Talking about this game is not easy because their goal [scored from an offside position] means a lot at this stage, it changes the whole aspect of the semifinal.
"We are angry but my experience tells me that we have to look forward. We will do our best in Kiev, we will prepare the game with the same concentration level as tonight's game.
"But we're capable of producing a great game just as we did against Wolfsburg and in Moscow against Dinamo.
"I'm optimistic because we are good enough to reach the final. They will surely be on the defensive side, we will go out there with our usual mentality."