David de Gea has been Manchester United's undisputed No 1 goalkeeper for over a decade - but as Erik ten Hag transforms the team, that status could soon be challenged.

Recent reports suggested Ten Hag still isn't entirely convinced the Spaniard is the right keeper for the system he wants United to play.

In the past, Ten Hag has relied upon keepers who are comfortable with the ball at their feet and passing the ball out from the back.

David de Gea's position as Manchester United's undisputed No 1 goalkeeper could be at risk

De Gea, 31, is also out of contract in the summer and it remains to be seen whether United offer him a renewal on the same terms of £375,000-a-week, if at all.

Despite his long-standing service and excellence between the posts during what has been a lean period for United in terms of silverware, De Gea may have to take a significant pay reduction to stay at Old Trafford.

Two potential successors to De Gea are the Porto goalkeeper Diogo Costa and Athletic Bilbao's Unai Simon.

Costa, 23, has a long-term contract with Porto until 2026 and United would likely have to match a reported release clause of £51million.

Simon, 25, has a contract through until 2025 with Bilbao and is likely to cost £25m or more to sign.

But would either of them actually offer an upgrade on what United already have in De Gea? Sportsmail takes a look...

SHOT STOPPING

De Gea has long been lauded for his shot-stopping abilities and it's fair to say the modern Manchester United would be even more diminished if not for his reflexes and reactions.

The fact he has been the fans' player of the year four times and the players' player of the year four times during his time at United just underlines his importance.

His shot save percentage over 11-and-a-bit seasons at United is a very respectable 72.5, according to fbref.com, but that has dipped to 67.4 in 12 Premier League games in the current campaign.

De Gea's return in the Europa League is a far more impressive 80 per cent, however, having played all five of United's group games.

There isn't too much difference with the two competitors. Costa averages 70.1 per cent in his 48 league matches for Porto, but that is at a high of 73.3 this season.

Simon has a healthy average of 71.9 per cent over his five seasons in LaLiga with Bilbao but that has dropped off from 74.8 last season to just 61.3 this.

That's despite Bilbao doing fairly well in the league - they're sixth in the table and within touching distance of the Champions League places.

GOALS CONCEDED AND CLEAN SHEETS

The 57 goals De Gea conceded in the league alone last season was the highest of his time with United - though that owed plenty to the shaky defence in front of him.

He only managed eight clean sheets in 38 league outings, which was substantially lower than in the majority of his seasons at Old Trafford.

Ten Hag has certainly tightened United up at the back, with the signing of Lisandro Martinez a notable factor, and De Gea should keep more clean sheets this time around.

Costa's clean sheet percentage was double that of De Gea's last season but the caveat is that he was playing for a champion team in the Portuguese Primeira Liga, which isn't considered one of Europe's top-tier divisions.

Simon's clean sheet percentage averages out at 30.6 per cent during his time with Bilbao so far, slightly less than De Gea.

Last season, when they came eighth in Spain, it was at 35.3, higher than the United stopper.

TOUCHES AND PASSING ABILITY

There has always been a perception that De Gea isn't comfortable with the ball at his feet in the same way as Liverpool's Alisson Becker or Manchester City's Ederson are.

It has been suggested this could be a barrier to his status as United's No 1 going forward under Ten Hag. De Gea has always refuted the claims, pointing out he has to play the ball out with Spain.

The stats show a clear rise of his involvement with the ball at his feet since Ten Hag came in, from an average of 26.8 touches per game under Ole Gunnar Solskjaer and Ralf Rangnick in 2021-22 to 31.5 this season.

But these numbers are some way below Costa's averages of 38.3 touches per game last season and 43 this. It suggests the Porto stopper is trusted by his team-mates with the ball at his feet.

In terms of passing out from the back, De Gea currently has a 100 per cent completion rate for passes of between five and 15 yards, and 98.9 per cent for passes between 15 and 30 yards.

Costa would offer only a fractional improvement on De Gea - he was perfect with short passes last season and averaged 98.9 for 15-30 yard passes.

He is, however, more accurate when it comes to longer passes of over 30 yards but this would surely defeat the point of Ten Hag's exercise?

Simon would also offer reassurance with the ball at his feet. His medium-range passing is running at 99.4 per cent this season, following on from 98.5 per cent completion last season.

It suggests he rarely gives away possession playing the ball out to a defender or midfielder when tasked with getting the team going.

So while both Costa and Simon would offer a minor improvement on De Gea's passing stats, the gulf isn't as wide as you'd expect.

PENALTY SAVES

De Gea came in for much mockery when he failed to save any of Villarreal's 11 penalty kicks in the Europa League final shoot-out in 2021 - before missing the decisive kick he took.

He isn't renowned as the best penalty saver but has kept out 13 during the course of his career, as opposed to conceding 58 (excluding shoot-outs).

After that Europa League disappointment, last season saw De Gea save his first penalties since 2016, keeping out Mark Noble's late spot-kick in United's win at West Ham and then repelling from Ismaila Sarr in the 4-1 loss at Watford that led to Solskjaer's sacking.

De Gea has already conceded from 12 yards against Chelsea and Real Sociedad this season.

It's a much smaller sample size but Costa has the makings of a penalty saving master. He has kept out three during Porto's Champions League group stage campaign, preserving his clean sheet on all occasions.

Simon has also kept out a handful of penalties during his Bilbao career but the last four he has faced have beaten him.

CROSSES

De Gea was criticised in his first few months for not being strong enough to cope with the physical demands of the Premier League as he was bullied at crosses.

It isn't really a facet of his game that has developed a great deal. The stats over the last six seasons show he stops or claims just two per cent of the hundreds of crosses that come into the United box.

Most of the time, De Gea is happy to leave it to someone like Harry Maguire to clear the aerial danger despite standing 6ft 4in tall.

Costa, also 6ft 4in, seems to have a bit more authority inside his penalty box, dealing with 7.5 per cent of crosses that come in, while Simon (6ft 3in) also has a higher future of 4.7 per cent at Bilbao.

It does suggest both would make for a greater presence than De Gea in the penalty box.