David de Gea's future at Old Trafford has come under scrutiny on numerous occasions down the years, from questions over whether he could handle the physical element of the Premier League in the early stages of his Manchester United career to the constant links with Real Madrid.
Had it not been for a dodgy fax machine then the Spaniard may well have left for the Bernabeu a while ago, but there is no doubting how important he has been to United in recent seasons.
De Gea has widely been regarded as one of the world's best goalkeepers during that time, being named in five PFA Teams of the Year and winning the Match of the Day Save of the Season award a whopping five times.
Quite where United would have been in the post-Sir Alex Ferguson era without De Gea is a thought which will make most of the club's fans shudder given that he has been named United's player of the season four times too.
However, this summer his place looks set to come under a new threat from Dean Henderson, who is currently on the Red Devils' books but has shone on loan at Sheffield United.
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Henderson's rise has come just as De Gea has suffered a dip in form and, having been undroppable for much of the last eight years, the Spaniard has now seen his place in the United team seriously questioned.
The statistics do not read well for him; since the start of last season no player has made more errors leading directly to goals than De Gea, the latest of which saw him gift a goal to Dominic Calvert-Lewin in a 1-1 draw with Everton.
On the flip side, Henderson has gone from strength to strength over the last two campaigns, helping Sheffield United to promotion last term and further enhancing his reputation this season as the Blades push for a shock European spot.
There is very little to separate the two teams as things stand - Man United sit two points clear of Sheffield United, but Chris Wilder's side have a game in hand - while the Blades have conceded 25 goals to the Red Devils' 30.
The individual form from the two players also has Henderson out in front, and on a purely statistical basis there is a very strong argument that he should usurp De Gea as United's number one next season.
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The 23-year-old England hopeful has kept more clean sheets (10-8) in fewer games (27-29), while he has also conceded fewer goals, shipping 22 compared to 30 for De Gea.
Somewhat surprisingly given Man United's backline - which includes the most expensive defender in history and another £50m+ man in Aaron Wan-Bissaka - De Gea has had more saves to make than Henderson, although that is a close one with the Spaniard leading 76 to 70.
However, Henderson's save success rate stands at 76.1% compared to 71.7% for De Gea, while the Sheffield United shot-stopper has also made more punches, high claims and sweeper clearances, in addition to saving one of the two penalties he has faced.
Henderson has also made more clearances and won more aerial duels than De Gea, and the Man United stalwart has made three errors leading directly to goals, whereas Henderson has made just one.
Those stats are all fairly conclusive, then, but there is one aspect where De Gea boasts a significant advantage over his potential successor, which could have a notable impact on how Ole Gunnar Solskjaer's side play.
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Henderson has made exactly 100 more passes than De Gea this season, but just 35% of those have found their target - a much lower figure than De Gea's 71% success rate.
Of course, the respective styles of play from the two teams should be taken into account and Henderson would be likely to improve that ratio playing more short passes - as things stand he averages 7.1 long balls per Premier League game whereas De Gea's figure stands at just 2.4 per game.
In most other aspects De Gea has had to play second fiddle to Henderson this season, though, and at the very least there will be a question for Solskjaer to ask of his two goalkeepers this summer.
Man United already have arguably the best back-up keeper in the division with Sergio Romero - a 96-cap Argentina international - and it looks as though Henderson will either return as number one or be shipped out again, possibly on a permanent basis this time.
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De Gea also has enough credit in the bank from past heroics to see him through a season or two below his usual standard, but there are other elements aside from the stats which could also make Henderson more appealing.
The Red Devils have been linked with a number of big-money moves this summer - Harry Kane and Jadon Sancho among them - and De Gea would still command a hefty transfer fee, not to mention getting the Premier League's most expensive wages off their books.
The Spaniard is also now 29; by goalkeeping standards that is still young, but Henderson is outperforming him at the age of 33 and could feasibly be the club's number one for the next decade or more should he maintain that form.
That would be some rise to prominence for a player who has been shipped out to the National League North, League Two and League One already during his Man United career, but there is no doubt that Henderson has earned his shot at the big time.
