Napoli sports director Pierpaolo Marino was sorry to see Edy Reja leave this week.
The 63-year-old Reja had been at Napoli since January 2005 and helped guide the club from the Third to the First Division.
"It's an inconceivable crisis," Marino told Il Napoli. "I say this sincerely, I am really very sad. I wish Donadoni good luck but it's upsetting that a man like Reja should go after giving Napoli so much.
"There probably were problems in the dressing room he couldn't resolve."