The Bianconeri suffered a shock 2-0 defeat at the Stadio Via del Mare after Gigi Buffon was sent off in the opening 12 minutes, but the scoreline could've been a lot worse.
"We got the wrong approach from the start," slammed Del Neri. "The team was very arrogant. This is a defeat that should make us think carefully, as we should've been more intense and taken charge.
"Lecce were always first to the ball and we deserved to lose. In fact, we're lucky it only ended 2-0. We are unable to face supposedly 'easy' games with the right concentration.
"Now our objectives seem a long way away. We cannot afford any more mistakes. It's a shame, as we were on the right path, but today we had no excuses for this performance."