Al Ittihad have won just six of their 12 league games this season and the final straw appeared to come in a 2-0 AFC Champions League loss to Air Force Club of Iraq on Monday.
This run stretches to just two wins from their last nine in all competitions and reports claimed tempers had flared between players and manager.
Revelo reports that Ballon d'Or winner Karim Benzema and Nuno exchanged insults in the changing room after an embarrassing defeat to Al-Quwa Al-Juwiya.
In a statement on X, Al-Ittihad said: "The club has announced the end of its contract with Portuguese coach Nuno Santo.
"This decision comes after a comprehensive technical evaluation of the past phase during which he was in charge of coaching the first football team."
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Nuno had been in charge of Al Ittihad since July 2022, taking the job eight months after being sacked by Tottenham.
In 56 total games in charge of the Saudi club, he lost just eight of them.
Reports also suggested that Al Ittihad may bring in a French manager to appease Benzema, with Laurent Blanc among the candidates.
He was a key man for Blanc when he was in charge of the French national team between 2010 and 2012.
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