Erik ten Hag criticised his defenders for 'easy giveaways' in their 4-3 loss at Bayern Munich in the Champions League on Wednesday evening.
Andre Onana was at fault for letting Leroy Sane's opener slip past him and Jamal Musiala found it far too easy to dash past defenders in the run-up to Bayern's second.
A handball from Christian Eriksen gave away a penalty for Harry Kane's goal and Bayern's third, and the marking could have been better to prevent Mathys Tel from adding a fourth.
After a night where United were torn apart and flattered by the scoreline, Ten Hag laid the blame at the feet of his back line - and refused to pin too much on Onana.
He said: '[I'm] disappointed and when you score three goals in Munich, at the least you have to take a point and we didn't. And you have to look in the mirror because the goals were easy giveaways.
'We were, in the first 25 minutes, better in the game than Munich and then that goal, it was so easy and it was not only Andre. If you see how easy Sane is going through and that has to do with determination, you don't let players through so easy.'
He demanded that his players show more willingness to 'sacrifice and suffer' after a run of four defeats in six games, with three losses on the bounce.
He said: 'That is the point - we have to cross the line as an individual and as a team to win games because it started there.
'That's what I mean, you have to suffer, sacrifice in situations, to give everything and to stop that and only when we get that in are we going to win games.
'Of course, he [Onana] knows he has to stop the ball but the way Sane came through can't be. And the second goal; it's almost similar over the other side. How easy players come through our box and to finish, it can't be.Read on m.allfootballapp.com