Rashford was one of the players to be held responsible for the Red Devils' lack of fight for most of the game, as Pearce said the England star looked "like he had a fridge on his back".
He said on talkSPORT during the game: "Man United are under the cosh because too many of their players have jacked it in. Rashford half running back and Casemiro half running back.
"I'm not sure what Onana said when he has a rant at [Harry] Maguire in the summer but now is the time to have a rant at the back line, not just the back line but the whole team. Too many players who have given up the ghost and that is alarming. United are so off the pace and they are lucky that Bayern have not been more clinical."