Wes Brown believes communication and concentration are the two biggest factors behind Manchester United's suspect defence, as opposed to tactics or quality of personnel.
Ole Gunnar Solskjaer's men have been a mixed bag so far in 2020/21 and know they will need to be at their tightest to keep out a host of attacking superstars during Man Utd v PSG live on BT Sport this evening.
Former United defender Brown is growing increasingly frustrated with individual errors as opposed to the defence simply not being good enough.
He said: "I think there's been a lot of errors, you can see a lot of silly goals. The game in the Champions League against Istanbul, it was just a clearance and there was just no-one in sight.
"These are all just communication problems and concentration. People should understand that they're not bad players.
"They have been letting in really weak goals at times and a lot of it has come down to individual error.
"This, at a big club like Manchester United, just can't happen."
Brown was part of the triumphant treble-winning side during the 1998/99 season during which they won the Champions League, as well as the 2008 Europe-conquering team.
He has called on United's stars to focus on simply defending, getting back to basics and remember their primary duty, in a bid to stem the tide of errors.
Brown said: "Rely on defending, think about defending, as a defender, we would go out and our main thing was to just not let any in, regardless of what happened up front.
"We just wanted to do our jobs and I'm hoping that's what they want to do."
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