Man United manager Michael Carrick
Gary Neville highlighted worrying errors from Patrick Dorgu, Andrey Santos and Leny Yoro led to Manchester United conceding late at Everton.
Major concerns were raised about United's defensive issues, with Gabby Agbonlahor warning they will get found out in the Champions League.
Ainsley Maitland-Niles scores for Everton against Manchester United.3
Maitland-Niles ensured United missed out on victory by scoring a late screamer
Ainsley Maitland-Niles scored an outstanding equaliser in stoppage time on his Everton debut to seal a 2-2 draw on Sunday.
United thought they wrapped up three points in the 88th minute as Benjamin Sesko headed in from a Luke Shaw cross.
However, the long-range effort from Maitland-Niles flew past Senne Lammens and into the top corner to ensure the points were shared.
The result has left United with just one win from three in the Premier League this season, and club legend Neville highlighted the defensive fragilities from three players that led to the crushing blow.
"Manchester United are conceding two goals a game," he explained on his podcast. "From a United perspective, you can't concede two goals a game, they're on track to concede 76 goals if they carry on.
"They won't concede 76 goals, but the thing that I think needed to happen beyond the transfer window, with the questions that have been asked about the defence was that Manchester United, one, needed to win today. But secondly, they couldn't concede goals.
"There may be some people that lazily could say, 'They were two spectacular goals'. I mean, that last goal is a really bad one. It's a really bad one because they're on that far side, you know you've got Jack Grealish down on the left...
"Dorgu, for some reason, chases out and presses, isolated press. Santos then doesn't go over behind him and stays back, and it just gets played past Dorgu. It's a massive mistake, that.
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"It's a massive mistake from Dorgu, but he might have been told to go and press by Santos. I don't believe he will have done, it just strikes me with a lot of lack of communication.
"(Diogo) Dalot went off, and Yoro comes on at right-back. He's narrow and tucked in, and deep, as are the other back four players, and (Noussair) Mazraoui is at left-back, so United have had to change their back four again during the match.
Manchester United after drawing to Everton in the Premier League.3
Neville has explained the defensive mess that led to the goal
"Yoro coming in at right-back, I'm sorry, that for me highlights the problem, because he plays so narrow. If you look at what happens on that last goal, forget the last bit, the keeper can't do anything about it, it's a special strike.
"A lot happens before that goal goes in the back of Manchester United's net. When you're playing against a team, it's 2-1, you're away at Everton, at Hill Dickinson Stadium, you've got to push up, you've got to make sure that you don't get players sprinting off and doing stupid things.
"Dorgu sprints forward, the ball gets played past him, and Everton just drift down that left-hand side so easily. Santos doesn't get across, and then when Santos doesn't get across quickly enough.
"Yoro is deep and narrow, almost playing like a third/fourth narrow centre-back, waiting for the ball to go into the box.
"They could have stopped it at source, so that to me is a real error in the lead-up to that.
"I was screaming as it happened, because you know full well you're going to get the ball pumped into your box or you're going to get a shot against you, or you're going to get a team being desperate in the last few minutes.
Manchester United head coach Michael Carrick.3
United have been tipped for more defensive frailties in the Champions League
"So you have to make sure that you're organised, and United weren't organised in that last couple of minutes, and teams think they've got a chance against them."
United set for Champions League 'beatings'
Neville is not the only one concerned with the United back four, as Gabby Agbonlahor has also raised questions over their quality.
The talkSPORT pundit has even predicted them to suffer some heavy losses in the Champions League this season, with United beginning their league phase campaign against Sabah FK on Thursday night.
"Harry Maguire, I thought he had a good game," Agbonlahor said: "I look at Lisandro Martinez, I'm not sold on him, I think he can be the weak link, especially when crosses come in.
"Luke Shaw, very good going forward, maybe not as good defensively yesterday. And Dalot, when Jack Grealish came on, he was giving away fouls, he had to get taken off for Yoro, who came in on that right-hand side.
"Yoro, big-money signing, he should be starting, he should be saying to himself, 'I should be starting in this side.'"
"I think they're going to get some beatings in the Champions League," he added. "With that back four, and the quality in the Champions League, they're going to get found out."