The 22-year old winger has joined the Baggies on a season-long loan pending international clearance with manager Steve Clarke very excited about his impending arrival.
"He is an exciting prospect who will add something different to our squad," said Clarke.
"We believe he has got the raw talent to make an impact here.
"This is a big move for Yassine. We'll have to be patient with him as he settles into a new country and gets to grips with the demands of the Premier League."