He leaves the Dubai club, at least for now, after only four league games.
Wasl made the announcement on their official Twitter account, writing: "Due to his current health condition, Bruno Metsu has requested to be relieved from his duties as head coach of Al Wasl.
"The Al Wasl board has accepted Metsu's request and thanked him for all he has given, wishing him a speedy recovery and best wishes."
Gilles Morisseau, Metsu's French assistant, will continue as caretaker coach. He led Wasl to victories over Al Jazira and Ajman in the time since Metsu has been unable to continue with the club.
Neither Metsu nor Wasl have confirmed the nature of his illness. The club's next match is home to Al Dhafra tomorrow.
Wasl football officials have credited Metsu, 58, for restoring stability in the side after the firing in June, after one tumultuous season, of Diego Maradona.
Metsu is well known in the country for his role as coach in two of the UAE's most significant football victories: the 2003 Asian Champions League, won by Al Ain; and the 2007 Gulf Cup championship captured by the senior national side.
Metsu, easily recognisable by his long hair and easy demeanour, was visited in American Hospital in Dubai by numerous football officials, including members of the Wasl board, Quique Sanchez Flores, the Al Ahli coach; Walter Zenga, the Al Nasr coach; and Maradona, now an "honorary ambassador of sports" with the Dubai Sports Council.
Metsu is best-known internationally for leading Senegal's opening-match upset of holders France in the 2002 World Cup.
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