Zamalek have accused referees of favouring arch rivals Ahly and said they would withdraw from the Egyptian Premier League in protest at what they called "disastrous refereeing errors".
The Cairo club, whose hopes of defending their Premier League title faded after falling eight points behind leaders Ahly with five matches remaining, were incensed after Arab Contractors had two players sent off for dissent in a game against Ahly on Wednesday.
Zamalek released a statement even before Ahly's match against Contractors ended, saying the Egyptian Football Association's refereeing committee intended to "gift the title" to their bitter foes.
"The club's board of directors, under the leadership of chairman Mortada Mansour, decided not to continue this league competition as long as the refereeing committee and its head Gamal El-Ghandour remain in their position," Zamalek said.
"The decision comes due to disastrous refereeing errors. At a time when an illegitimate goal by Maqassa against Zamalek was allowed to stand [in Sunday's league match], Contractors had two players wrongfully dismissed against Ahly.
"This clearly shows an intention to gift the title to Ahly amid a dishonorable competition."
Two Contractors players received straight red cards for protesting a goal by Ahly striker Malick Evouna midway through the first half. The Gabonese international doubled his side's lead with a simple finish three minutes before the break.
Zamalek's outspoken chairman Mansour issued similar threats in the past for different reasons but he usually reneges on such stunning decisions. The team are scheduled to face ENPPI on Thursday.
The White Knights claimed a rare domestic double last season and won the league for the first time since 2004 to end Ahly's eight-season hegemony.
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