Lorenzo Insigne had no explanation for Napoli's below-par performance at Shakhtar Donetsk that resulted in a 2-1 defeat.
Having been drawn into the tricky Group F, which also includes Manchester City and Feyenoord, in the Champions League, the Serie A side could have done without a loss in their opening game.
But Shakhtar were good value for the three points as they netted through Taison and Facundo Ferreyra before Arkadiusz Milik's penalty made a fight of the closing stages.
Napoli had chances to grab an equaliser, but Insigne conceded his side made errors across the 90 minutes that they must now address.
"We knew that Shakhtar were a good side as they have quality players in attack," he told Mediaset Premium. "I honestly don't know what we got wrong and why we played like this.
"During the week, we will discuss it with the coach and see what mistakes we made so that we can correct them.
"Perhaps we believed a little too late that we could come back, but we had chances and didn't make the most of them. We had the opportunities to equalise. It's a pity.
"We've got to get our heads down and work hard to improve on the errors we saw today."
Maurizio Sarri mixed up his team selection, leaving star man Dries Mertens on the bench, but Allan – also a substitute – had no issue with the decision.
"We are all ready to play and therefore all ready to be on the bench, too, as there are many games," he added.
"I respect the decision of the coach. There are many quality players and we've always got to be ready."
21 de enero 2018
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|PSG star Mbappe injured in goalkeeper collision|
|Smith rejects ball tampering talk|
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|Brady active with taped throwing hand for AFC Championship Game|
|Cagliari 1 AC Milan 2: Kessie at the double in comeback win|
|Watford hire Javi Gracia as Marco Silva successor|
|I am happy with our squad - Pochettino denies Malcom rumours|
|Not much changed - Zidane boosted by clinical Madrid|
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|Saracens edge into last eight as Wasps and Ulster miss out|
|Selfie or stitches? Ronaldo bloodied after Madrid brace|
|Heynckes hails Bayern win: This is what sets us apart|
|Southampton 1 Tottenham 1: Kane earns visitors a point|
|Silva assured of chances at AC Milan after latest first-team snub|
|Saracens scrape into Champions Cup last eight|
|Goretzka´s Schalke return marred by abuse|
|Real Madrid 7 Deportivo La Coruna 1: Seven-up for Zidane´s men as Bale shines|
|McIlroy ´in really good shape´ after Abu Dhabi return|
|Muller brings up 100 Bundesliga goals in Bayern win|
|Dimitrov places Kyrgios among tennis´ most talented after Melbourne classic|
|Bayern Munich 4 Werder Bremen 2: Lewandowski & Muller at the double to spare champions´ blushes|
|Do Arsenal or Man Utd get the better deal? Sanchez v Mkhitaryan in Opta numbers|
|Edmund: I can win Australian Open|
|Pele ´fine´ and in ´no pain´ after reported health concerns|
|Dimitrov can go all the way, claims Kyrgios|
|Dominant Wozniacki sets up Suarez Navarro showdown|
|Brilliant back nine sees Fleetwood retain title|
|Surgery pushes Pocock´s Brumbies return back three months|
|No mercenary? Sanchez endorses article defending imminent Man Utd move|
|Allegri expects Buffon to be ´fully recovered´ within a week|
|Atletico Madrid confirm Costa hamstring injury|
|Thisara stars as Sri Lanka stay alive in tri-nation series|
|Atalanta 0 Napoli 1: Mertens ends drought to keep visitors top|
|Nadal through to meet Cilic as Dimitrov downs Kyrgios|
|Dimitrov holds off Kyrgios as wait for home champion goes on|
|Alexis Sanchez boards plane ahead of reported Man United medical|
|Smith not sour over controversial dismissal|
|Buttler the difference for England, says Morgan|
|Hamburg dismiss Gisdol after fourth loss in a row|
|Brilliant Buttler century sets up England series win|
|Melbourne City 5 Adelaide United 0: Budzinksi & Vidosic braces inspire emphatic win|
|Marco Silva sacked by Watford following ´significant deterioration´|
|Nadal promises greater aggression in the last eight|
|Deschamps knows my thoughts - Lucas Hernandez hints at France decision|
|Nadal battles past Schwartzman in Melbourne|
|Wozniacki: I have nothing to lose|
|Impey claims historic Tour Down Under win|
|Rockets end Warriors´ 14-game road winning streak|
|Klopp: Liverpool wouldn´t sell to rivals during season|
|Spence retains IBF welterweight title with TKO of Peterson|
|Wozniacki cruises into Australian Open quarter-finals|
|Giggs keen to help Bale overcome injury woes|
|Harrison key to containing ´monster´ Fournette|
|Klopp in no rush to replace Coutinho|
|Cook leads, Rahm in contention in California|
|Cavaliers booed after abysmal first quarter|
|Titans hire Mike Vrabel as new head coach|
|Brive deny Worcester after stadium swap|
20 de enero 2018
|Malcom dreams of Premier League but remains unsure of future|
|Guardiola sets target of 10 wins to guarantee title|
|Championship Review: Millwall break Leeds hearts in seven-goal stunner as Wolves lose|
|Messi and Pique welcome Coutinho to Barcelona training for first time|
|Thauvin ´very happy´ at Marseille|
|Guardiola salutes ´outstanding´ Manchester City|
|Saracens still not safe, Scarlets battle through|
|Watford still battling relegation from the top half, insists Silva|