Manchester United still need four or five more players to challenge the elite again, including a "world-class centre-back", according to Gary Neville.
United improved on a dismal sixth-place finish in 2018-19 by securing third place in the Premier League and Champions League qualification last season.
Ole Gunnar Solskjaer has been able to add the likes of Harry Maguire, Aaron Wan-Bissaka and Bruno Fernandes to his ranks since being named the club's permanent manager in March 2019, all of whom have made a huge difference to the squad.
However, despite the improvements made over the past 12 months, the Red Devils still finished 33 points behind champions Liverpool and 15 adrift of second-place Manchester City, while their trophyless run was extended to three years.
Solskjaer has been tipped to add to his ranks once again in the summer transfer window, with the likes of Jadon Sancho, Harry Kane, Dayot Upamecano and exit-bound Barcelona superstar Lionel Messi among those being linked with moves to Old Trafford.
Goal has reported that Donny van de Beek looks likely to be the first man through the door, as United have agreed on a £40 million ($54m) deal with Ajax for the talented midfielder, but Neville is growing frustrated with the club's lack of urgency in the market.
The ex-Red Devils full-back believes his old club should be prioritising the signing of a new central defender, but says Solskjaer will need at least three new additions in total to start closing the gap on Liverpool and City.
"The Manchester United squad, as it stands today, cannot challenge for the Premier League title this season," Neville told Sky Sports.
"The squad needed four or five improvements and it still needs four or five improvements. I've been saying that for a year and I've even nominated the positions I feel they need to improve.
"They have to sign a world-class centre-back. For me, another midfield player. I also think a right-winger, a centre-forward and you have to look at left-back because of Luke Shaw's injuries and the fact he has obviously been in and out of the team in the last two or three years.
"So, I think there are definitely four or five players required and to not get three I think it would be a problem because of what the other clubs are doing. If Liverpool get Thiago, if Manchester City do what they are looking like they are going to do and with Chelsea doing what they've done, they are your competitors and they all look like they are improving and moving forward.
"So, United have to do business but I do believe more in the strategy of what's happening, they just have to get the deals over the line. That's not always easy but they have to try and do it quickly to give Ole the time to build to get this team moulded for the start of the season."
Neville went on to address United's well-documented pursuit of Sancho, insisting there are plenty of alternatives targets for the club to consider should a deal for the Borussia Dortmund starlet prove to be out of reach.
"The fans I speak to aren't saying we desperately want Sancho," he added.
"They are saying we want the right calibre of signing brought into the club. It could be anybody that fits that bill. Yes, Sancho may fit that bill, but I'm not sat here as a United fan thinking I desperately want him.
"It could be any number of players that become available that would improve United. If Harry Kane became available, and Tottenham fans will be saying why are you trying to get him out of Spurs again, but if he became available, he'd obviously improve United's squad. So it doesn't have to be a certain player."