Are Manchester United heading for a defensive disaster? Andre Onana is already on Harry Maguire’s case, Erik ten Hag moans about sloppiness in play and only one injury can wear out the back line

New midfielder. Tick. New goalkeeper. Tick. New striker. Almost tap.

Erik ten Hag has every reason to be pleased with Manchester United’s transfer business so far this summer.

With two weeks to go until their Premier League campaign kicks off, United already have Mason Mount and Andre Onana through the door and the £72 million signing of Rasmus Hojlund should be completed this week.

It’s all very civilized and a stark contrast to 12 months ago when key additions Casemiro and Antony arrived after the season got off to a bad start.

While everything looks quite positive, problems can crop up at the big clubs and now it is United’s defense that gives Ten Hag cause for concern.

Signing a new central defender has always been low on United’s priority list this summer. Sure, they needed the players they signed more urgently.

But with only Lisandro Martinez, Raphael Varane, Harry Maguire and Victor Lindelof on the books as senior players – and Maguire being linked with a departure this summer – United are looking a little worn at the back.

Only one injury or suspension can leave a gaping hole in Ten Hag’s defence, forcing left-back Luke Shaw or one of their midfielders to step in.

That’s why 35-year-old Jonny Evans is back in a red shirt on their pre-season tour of the United States. Signed as ‘cover’ for a few matches, the veteran could still earn a one-year contract.

This lack of depth would leave United looking vulnerable at the best of times, but even more so as they try to implement a new style after Onana’s arrival between the posts.

The Cameroonian goalkeeper, who joined from Inter Milan for £47 million, is known for his comfort with the ball at his feet and can often be found 30-40 yards from goal looking for the perfect pass.

It indicates that Ten Hag’s side will be more inclined to build from behind in the coming season – but there have been teething problems.

That was evident in Sunday-evening’s 3-2 defeat to Borussia Dortmund in Las Vegas, the final leg of United’s four-game US tour.

A frustrated Ten Hag described United’s sloppiness on the ball as ‘inexcusable’ after Dortmund gained possession in dangerous areas on more than one occasion.

Lindelof went straight to a yellow shirt ahead of Donyell Malen’s second goal – just seconds after his first.

Maguire got a blast from Onana after his limp pass from defense led to a save from Sebastien Haller by the keeper early in the second half.

And Aaron Wan-Bissaka was at fault for a misplaced and ill-advised pass into the field that led to Youssoufa Moukoko scoring what turned out to be Dortmund’s winner.

United never looked comfortable building under pressure from behind when David de Gea was their keeper, and on this evidence there is still plenty of work to be done with Onana if Ten Hag is to adopt that style.

With just two weeks of training – and two friendlies, against RC Lens and Athletic Bilbao – before the season opener with Wolves on August 14, there is still a lot to improve.

Frankly, it was not United’s first-choice central defensive combination to be seen in Las Vegas.

Varane sat out the game as a precaution and Ten Hag started with Maguire and Lindelof, who were replaced on the hour mark by Evans and Martinez.

Assuming everyone is fit and available, it’s Varane and Martinez who take on Wolves in two weeks.

Those two should be most comfortable with the defensive ball game approach and will get used to Onana actually moving behind them into the midfield base like a sweeper keeper.

In last week’s 2-0 friendly defeat to Real Madrid, Onana spent much of his debut 40 yards from his line, serving as 11th outfielder and confidently providing another passing opportunity for his defenders.

Onana and Martinez played together at Ajax, so know each other’s weaknesses on the field. Varane is one of the best in the world and should be easy to adapt.

Maguire has shown, playing for England, that he can carry a ball powerfully out of defence. His deliberate runs in midfield were indicative of the Three Lions’ run to the European Championship final two years ago.

But the former captain has also made mistakes in pressing at the back and is not a natural when it comes to passing out.

There is interest in Maguire from West Ham, with an initial £20m bid rejected, but the defender is adamant he will stay and fight for his place. Given the lack of options, you can’t blame him.

There have always been question marks at Lindelof, but Ten Hag seemed to favor the Swede over Maguire last season and he will play full again.

The worry is that if Martinez or Varane are injured – the Argentine broke his midfoot and missed the final weeks of last season, while the Frenchman was out for two spells – United will have defenders less familiar with the new style.

Club legend Rio Ferdinand has already warned fans to ‘expect mistakes’ in the coming season as Onana settles in and United’s defense gets used to him. He could be right, it will take time to adjust.

So should United now look for defensive reinforcements?

Hojlund’s signing will bring United’s spending to nearly £170m this summer, while the FFP-friendly budget given to Ten Hag was initially around £120m.

It means players have to be sold to balance the books and even then the money for a new defender will be severely limited.

Potential targets have also disappeared from the market. Jurrien Timber, who worked at Ajax under Ten Hag, has joined rivals Arsenal, while Kim Min-Jae, a target earlier this summer, moved from Napoli to Bayern Munich.

So United may have to make the most of their current pool of centre-backs simply in the hope that they stay fit and adapt quickly to a new goalkeeper and a different way of doing things.