Al-Somah, 36, joined Wydad under the special transfer window granted to clubs involved in the tournament, which runs from 14 June to 13 July.
Following his departure from Saudi Arabia’s Al-Orobah, Al-Somah is expected to join the Wydad squad's training camp in the US within hours, under head coach Mohamed Amine Benhachem.
Wydad, winners of the 2022 CAF Champions League, have strengthened their roster ahead of the global competition by adding Moroccan international Nordin Amrabat, Burkinabé midfielder Aziz Ki, and forward Hamza Hanouri.
The Casablanca-based team landed in the US earlier on Tuesday and will face European champions Manchester City in their opening match on 18 June.
The expanded 32-team Club World Cup, featuring clubs from across all confederations, is being staged for the first time in the United States.
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