Zola acted as No2 to the current Juventus coach.
"At the beginning the players were very much behind everything that we were saying, they were brilliant," Zola told beIN SPORTS.
"They were following everything, but then as the weeks passed due to the repetition and the amount of games they were playing, the players got tired and they also got bored in a way.
"But boring is part of our job. Sometimes you need to get bored but when you get bored you persist in what you're doing and you get better.
"They were talented players, like Hazard and Willian, players who know how to win games on their own, but they were suffering from the type of exercises and type of training we were doing - but it was necessary for the others," Zola added.
"I'll be honest, they were brilliant because they got bored, but they kept doing it throughout and that was the reason why when everyone was dropping we were going up towards the end."