Giggs warns their gaffer has gained enough knowledge to represent a threat to the Reds.
"Mark's managed quite a few clubs now so he's not a new manager anymore. He'll have them well drilled and well prepared, just like the majority of teams that come to Old Trafford. They'll make it difficult for us," Giggs told ManUtd.com.
QPR are the third relegation-threatened side to meet United in the last four games, following the Reds' victories over Wolves and Blackburn Rovers. Giggs thinks QPR could prove to be the toughest of the lot to take on, given the character of his fellow Welshman and the work he has done so far at the West London club.
"He's a fighter and he has good staff around him. He made some good signings in the January transfer window and has a lot of quality in the side . QPR will be organised on Sunday and he'll have them working hard."