An Adelaide United director says he's shocked at the sudden resignation of Michael Petrillo as chief executive of the A-League club.
Director Bruno Marveggio says Petrillo's decision took everyone at the club by surprise.
Petrillo, who had been with United since 2005, said in a statement the "timing was right to depart" without elaborating on the reason.
He will leave at the end of the month.
"The decision comes as a complete shock to everyone associated with the club," Marveggio said in a statement.
"We respect Michael's decision ... we'll begin the search for the best person who can continue to take this football club forward."
Petrillo was United's founding chief executive officer in 2005, becoming football director two years later.
In 2009, he helped establish North Queensland Fury before returning within six months to Adelaide as football director, then CEO again.
Petrillo said it was a difficult decision to quit United.
"But after 10 years I thought it was the right time to make the change now before the start of the new season to allow a period of transition," he said in a statement.