The FC Barcelona forward who's impressed during his temporary spell at domestic rivals Alaves this season sought to switch his international allegiance from Spain in order to represent the African nation.
However, FIFA ruling has bound the switch from taking place due to the 22-year-old appearing in 13 minutes of competitive football for La Roja during a European Championship qualifier against Macedonia in September 2014.
Both parties applied for a special dispensation from CAS over the ruling in hope of the technically gifted forward to be roped into the Atlas Lions World Cup plans in Russia next month.
According to reports on BBC Football, the board members of FIFA are studying a new proposal to create a more flexible ruling in future cases, but this hasn't overturned to ruling from the Court.
"Such decision is now confirmed and the request to change the sporting nationality of Munir El Haddadi from Spain to Morocco remains denied," CAS revealed in an abrupt statement.