Nani was always in Ronaldo's shade at United. He came from the same club and the same country, played in a similar position, so he had to live with the comparison until Ronaldo left for Madrid. After Ronaldo left, it was hoped that Nani would step up and become United's best winger, but it never happened, and he didn't win the trust of neither Sir Alex or David Moyes. And apparently not van Gaal's trust, either. Going back to his mother club is maybe a good move, wouldn't be surprised if that move is made permanent.