Napoli went to the Etihad Stadium for Tuesday's eagerly-anticipated showdown against Pep Guardiola's Manchester City and lost 2-1 in an absorbing European encounter.
Sarri's men backed up that performance with a 0-0 stalemate at home to Inter in a top-of-the-table clash in Serie A.
And the 58-year-old head coach believes Napoli care more about domestic honours as they look to dethrone six-time Italian champions Juventus for their first Scudetto since 1989-90.
"To be honest, I see my team more motivated in Serie A compared to Europe. We played at a high level of determination for 95 minutes, whereas in Manchester it was for 55 minutes," Sarri told Mediaset Premium.
"City have an extraordinary technical and tactical level, but the feeling I get is that the players care more about Serie A.
"The Champions League is tiring, but it's also a wonderful thing to take part in and we ought to give it our best. We'll pay whatever price we need to.
"I think it's a sub-conscious thing. If in our minds we feel more competitive in Serie A than in the Champions League, that might be a difficult thing to shake off.
"After all, we don't have that much of a chance to go all the way in Europe, but we do want to put in a great tournament performance."
As for the match against second-placed Inter, Sarri added: "Considering the game, the shots on target and territorial domination, we are to consider it two dropped points tonight.
"However, if we continue with this level of performance, few teams will be able to get points against us."