United lost their opening match 2-0 against Hull City, but they bounced back strongly with a 5-2 win over Ipswich Town at Old Trafford.
Carrick’s side look to be back to their best but a disappointing 2-2 draw with Everton on Sunday means that the Red Devils now sit 11th, with 6 goals conceded in 3 games.
United are back in action on Thursday, making their return to the Champions League against Azerbaijani minnows Sabah before facing rivals Manchester City on Sunday.
Ahead of their next game, Neville has pointed out United’s biggest flaw as the club continue to leak goals and fail to keep a single clean sheet.
"Conceding goals will hunt them and chase them down the road. I'm not sure how Carrick will deal with it as he's already got his best back four on the pitch. Why did Shaw and Dalot go off with five minutes to go? Ruben Amorim and Erik ten Hag changed their back four too. You can't be changing your back four. There's not much behind the first choice. So you can't change it.
"Manchester United are conceding two goals a game, you can't concede two goals a game. With the questions asked since the transfer window regarding the defence, United needed to win today and they couldn't concede goals. Lazy analysis will say they conceded two spectacular goals.”
Teams have more belief against United
Neville continued on United’s poor defender and revealed that he believes every side will believe they have a chance to score.
"Teams think they have a chance against them. I played in a Man Utd team where teams, in the period between Peter Schmeichel and Edwin Van Der Sar, did feel they had a chance against us at Old Trafford and we weren't quite good enough defensively.
"Teams have the feeling that they can score. That's a horrible place to be at."
The Red Devils' net spend across the transfer window finished at £118m as they brought in the likes of Andrey Santos from Chelsea, Youri Tielemans from Aston Villa and Carlos Baleba from Brighton.
No defensive signings were made and fans are starting to worry that Carrick has a real lack of quality at the back as they enter the Champions League this week.