Napoli stand on the verge of becoming the first team to clinch a last 16 berth after just three games.
Successive Group B wins over Dinamo Kiev and Benfica means Napoli stand on the verge of becoming the first team to clinch a last 16 berth after just three games.
Napoli will make history if they beat Besiktas at the San Paolo on Wednesday, and Benfica and Dinamo draw in Lisbon.
It is an impressive start by the Azzurri, but contrasts sharply with Napoli's domestic form: consecutive league setbacks to Atalanta and Roma has already left them seven points behind leaders and champions Juventus.
Sarri admitted his team's focus on the Champions League came at a price, but insists they are working to redress the balance.
"I have total faith in the squad, we're well aware of where we're making mistakes and we're working to get back to the way we were playing several weeks ago," he told media on Tuesday.
"The reality is, up till now the Champions League has been a bigger source of motivation for us compared to the league, and this is one of the problems we have to resolve.
"When you play such important games, psychologically you pay the price, especially when you have so many debutants in the competition as we do."
Last month, Napoli's impressive 4-2 win over Benfica came with a brace from Belgian international Dries Mertens and a 54th minute penalty from striker Arkadiusz Milik.
It was Milik's last goal for the club before he suffered a cruciate knee ligament injury while on international duty with Poland that is set to sideline him for several months.
Although Sarri brought Manolo Gabbiadini off the bench as a replacement, the 24-year-old Italian -- a more versatile forward than Milik -- ended up receiving much of the flak for a 3-1 defeat to Roma at the weekend.
Goalkeeper Pepe Reina believes it was not warranted, and called on fans to get behind Gabbiadini as Napoli look to eclipse the disappointment of their past two outings with another top performance in Europe.
"We've heard a lot of talk about Gabbiadini, but he's a top player, but it's up to the team to help him. I'm sure he will be a big help for us," said Reina.
After their Roma setback Reina was so incensed he wanted to face Besiktas the next day.
"It's important to get back to playing as soon as possible after a defeat. I would have played this game on Sunday," added the Spaniard.
"Two weeks ago it seemed we were the best team in Europe, now we're the worst.
"We're looking for a big performance tomorrow, we want to get back to playing in a clinical fashion in attack and with determination when it comes to defending."
Reina will make his 150th appearance in Europe on Wednesday, but says he hopes to continue.
"I'm getting old, but racking up 150 appearances in UEFA competition is something to be proud of," he said.
"But I'm looking forward. Let's hope I can make another 50."