He explained that manager Roy Hodgson 'made his views clear', and offered insight into the squad's current attitude.
"The gaffer had us in and made sure we knew it wasn’t good enough," McCarthy said. "He made his views clear and each and every one of us in the dressing room know it’s not been acceptable and it’s not good enough.
"We had a go tonight and unfortunately we’ve come away as losers. We need to try and pick ourselves up again and get going on Monday [v Wolverhampton Wanderers]."
McCarthy then focused more narrowly on tonight's meeting with the Red Devils, offering his view on a solid performance against in-form opposition.
He said: "I thought we went toe to toe with them. Obviously they’re pushing for Champions League spots and it’s just unfortunate a couple of big decisions didn’t go our way and it’s disappointing for each and every one of us.
"I thought, up until half-time, we matched them. Then the penalty decision goes against us and unfortunately we lose a poor goal.
"We know within ourselves that just before half-time we should be better and not lose a goal like that and then, second-half, we scored a goal and unfortunately VAR went against us again."
Full post-match reaction, highlights and both managers' press conferences will be available to watch free on Palace TV or the official Palace app. Either click here or 'Palace TV' within the app to enjoy.