Napoli boss Rafa Benitez questioned his players' desire after their Europa League defeat to Young Boys of Berne.
Young Boys won 2-0 to join Napoli at the top of their table.
"We lacked defensive intensity when they had scoring opportunities and that is why we conceded," Benitez said.
"I expected a different game. We controlled the match, but after the goal they clammed up. On the second goal we got the preventative marking wrong. This has happened in too many games now.
"In the first half we could've hurt them with our counter-attacks, but after going behind we lacked the intensity and pace to avoid their counters."
Benitez continued: "We lacked the desire to win the game a few times this season. We have to improve in that respect.
"Am I worried? No, many things that happened today need to be revised to improve. The intensity starts from the strikers, but often we lack it when defending and that allows our opponents to run on goal."
