Plus he won't get the protection from referees in England that he gets in Portugal. Always thought he was a different player before/after that cowardly assault from Carragher. Must be a weight off his mind playing in a league where he knows that defenders can't get away with persistently kicking lumps out of him.
He came back from that Carragher injury in average form (though still producing his goal/assist numbers)
But he started the next season (2011/12) absolutely on fire.
That goal vs City, a chip in the 8-2 vs Arsenal, assists and goals vs Bolton, and an absolute masterclass hammering Chelsea 3-1 (scored a wondergoal, won a penalty, tortured Ashley Cole and should have had a few assists if the finishing was better)
By some distance his best performance in a United shirt, perhaps in any shirt.
He was for some reason increasingly marginalised after the 6-1 loss to City as went more defensive, more back-to-basics, in general more
Young-and-Valencia. (This was Valencia's POTY season, Nani still produced more goals and more assists over the season despite being on the bench often)
By 2012-13 for some reason Valencia-Young was entrenched and with Kagawa and RvP's arrival, Kagawa and Welbeck entered the competition for the wing spots.
Then, after a really good performance vs Chelsea in that League Cup game (including another great solo goal) he was blamed for a defeat caused by us taking off our best player (Anderson) for Tunniclife (losing control of the game), and having two 18-year olds, one of whom made a terrible mistake in the 93rd minute (having already given away a stupid penalty)...SAF had to defend the kids but he picked on Nani who had given the ball away when alone in the opposition half more than a minute before they scored. IMO really bad management especially given that he knew Nani's personality pretty well by now.
His next big start was virtually the Madrid game at OT, assist and then Cuniyt Cakir.
Overall, I think a series of injuries (rather than one nasty one) affected his form, as did mismanagement (losing his manager's trust) and finally, some pretty rotten luck.