The Frenchman replaced Diego Maradona as coach of the Emirates side in July with a year still left on the former Argentina World Cup winner's contract.
The 58-year-old Metsu, who took Senegal to the quarter-finals of the 2002 World Cup, has been relieved of his duties after Al Wasl's board accepted his request to leave.
The Al Wasl board thanked Metsu in a statement for "all he has given during his time spent managing Al Wasl. We wish him a speedy recovery and send him our best wishes."
Metsu's assistant Gilles Morisseau will take over as caretaker manager in the interim period.
The Frenchman has had a colourful career coaching in the Middle East, enjoying success at both club and international level.
He led Emirates side Al Ain to the Asian Champions League title in 2003, in the first year of the new-look competition.
As coach of the UAE national side, he added the 2007 Gulf Cup of Nations to his list of honours.
Metsu also took host nation Qatar to the 2011 Asian Cup quarter-finals, where they were beaten 3-2 by eventual champions Japan.
He signed a two-year contract after being named as the replacement for Maradona, who was axed after Al Wasl finished eighth in the 12-team UAE league.
- Sports & Recreation
- Diego Maradona
- Al Wasl