Sarri was full of praise for Real Madrid after the match, but the 58-year-old has insisted that his team are still in the last-16 tie ahead of the return fixture in Naples early next month.
"We faced the best team in the world but it is a pity that we made so many mistakes with the ball because we don't usually do that," Sarri told reporters.
"While we were not at our best tonight I think we can compete with them if we play our best football. We have only a few chances now but we will try to give everything and see what happens."
Napoli will return to Serie A action with a trip to Chievo on Sunday afternoon.