The 22-year-old moved to la Liga on a season-long deal but United inserted a January recall clause into the agreement.
He has played predominantly on the right wing, an area United have struggled for a regular player, but Mourinho will not ask for the youngster back.
“They're playing in a total different system than us and he plays in a position that we don't have," he said. “We will need an update in relation to that.
“But the experience he's having, playing in a good competition, in a good club, in a difficult club because it's a club with big fanbase, with pressure around, I think is an amazing experience for him and we are happy to let him (stay) there."