The Azzurri lost 2-1 at the Stadio Via del Mare with both sides reduced to 10 men and Edinson Cavani will be suspended for the big game against Inter.
"I feel truly sad, as conceding a goal like that at the death from Javier Chevanton is a sign of great immaturity," said the President.
"Evidently we are not ready to compete at a certain level and aren't worthy of representing the Napoli colours.
"When I said we'd finish in fifth place, I wasn't joking. We cannot have players get themselves sent off and put an entire year's work at risk ahead of the game with Inter."