Napoli coach Rafa Benitez says they wasted too many chances after drawing with Europa League opponents Dnipro 1-1.
David Lopez struck for Napoli in the semifinal first-leg draw.
Benitez said: "Their goal was offside and clearly an incident like that changes the result of the game and the whole complexion of the semi-final.
"In any case, we had our chances and didn't take them. Now we have to win the away leg, but must be quicker and more precise, as we were in the second half.
"I expected the game to be like this, as Dnipro are a tough and organised team. We still had several opportunities to score and Dnipro found the net with their only attempt.
"In the first half we weren't quick enough and didn't attack the space, while we did decidedly better after the break and will fight the second leg the way we did against Wolfsburg.
"Now we cannot complain, so just have to focus on the trip to Kiev."