Undefeated Fiorentina escaped with a 1-1 draw at home to PAOK in Group K action at the Stadio Artemio Franchi on matchday four, after Italian defender Manuel Pasqual equalised two minutes from time.
PAOK substitute Maarten Martens had given the Greek visitors the lead seven minutes earlier, with their only shot on target.
And Fiorentina coach Montella was less than impressed by yet another lapse in concentration that has plagued the Serie A team - who are 10th in the league standings - throughout the season.
"Objectively I have to say our season so far is reflected in today's game," an irritated Montella told a news conference.
"We played with such great quality, but paid for lapses in concentration. I saw the harmony and relaxed enjoyment of football that I like, so we created many chances and if we had gone in front, it would've been a different game."
Montella added: "We suffered a little at the start of the second half, but with [Marko] Marin coming off the bench we improved.
"It's difficult to create more scoring opportunities than this, so what we can improve on is the finishing.
"I'd be more worried if the team didn't show that determination to avoid defeat at the end and in fact we pushed to the final whistle for a victory."
