Guendouzi has not played a part in any of Arsenal’s last five games, having been dropped by manager Mikel Arteta after clashing with Brighton and Hove Albion players shortly after the coronavirus enforced break.
The 21-year-old’s attitude has often been called into question and there are reports he could be moved on from the Emirates Stadium at the end of the season.
Casoni has urged the France youth international to turn a new leaf if he wants to fulfill his full potential.
"Guendouzi's problem is not physical and is not technical," said Casoni in quotes reported by Mail Online.
"It's his attitude, it's not good for the team or the coach. My relationship with him wasn't very good.
"I picked him for a cup game against Nice but he got booked early on. The ref told me at half time to warn Guendouzi: one more foul and you're off, but in the second half nothing changed.
"I was left with no choice but to sub him off. When I did, he refused to shake my hand."
"He took his job seriously, his training was no problem, and his character is to always want to win," said Casoni.
"Sometimes when he talks it's good. But sometimes he talks badly. He talks too much.
"His talent isn't in question, that's not the issue. He can be a top, top player and I think he can still succeed abroad. It's up to him to change his attitude."
Guendouzi joined Arsenal from Lorient in the summer of 2018 and he has made 34 appearances in all competitions this season.
