Traore, an attacking midfielder, joins from Association Jeunes Espoirs De Bobo-Dioulasso and is a full international for Burkina Faso.
He made his debut in September 2011, a few days before his 16th birthday, and made one substitute appearance at the 2012 Africa Cup of Nations.
"Traore is a great talent that the club followed for a long time before me," Mourinho said.
"I wanted to take him to pre-season to have a view of him for two or three weeks and play him in front of 60,000 to 80,000 crowds like we have in Asia.
"Now we could get him. We have a kid who in our opinion is one of the best talents of his age. I think he is ready to make an impact."
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