Domenico Berardi's penalty after eight minutes decided the match for the home side.
“We are not very well," De Zerbi told Sky Sport Italia after the match. “We are suffering physically and athletically.
“We are clinging to the top positions with our nails. In the first half we did better than the second. Creating chances against Benevento is never easy.
“There are times when you aren't brilliant, we will soon go back to being brilliant. We are growing and important players are recovering.
“Being there mentally for us, who are a small team, is crucial. [Fillip] Djuricic did well in the role of first striker due to his characteristics, he's not in top shape either, just like [Giacomo] Raspadori.
“We need to improve our game on Wednesday in Florence. If we don't go back to being the usual us, we will pay in the long run.
“But the players know this too. We are ambitious, we want to improve our position, but we must not forget that three years ago we started with a lot of young players.
“We are still young, including me. I don't want to put too much pressure on the lads. We must have fun and improve ourselves, aiming for the maximum."