Pearce was left unimpressed by Rashford's work off the ball
"United are under the cosh because too many of their players have jacked it in. Rashford half running back and Casemiro half running back," Pearce said on talkSPORT.
"I'm not sure what Onana said when he has a rant at 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."
As United were losing 4-3, Pearce also said during the Champions League defeat: "Too wide open, too regularly. Their goal to come back to 3-2 was a false dawn. They conceded four and that's what they deserved.
"As silly as it sounds, the score flatters United. What concerns me is that United almost stopped trying for about 15 minutes - even though they scored in that time."