Despite leading the Premier League's Golden Glove race with 15 clean sheets this term, the Spain international had displayed a propensity for costly mistakes.
De Gea's latest fatal error came in Sunday's 1-0 defeat to West Ham United, where Said Benrahma's strike hit the goalkeeper's palm before trickling into the back of the net.
The former Atletico Madrid man has now made four errors directly leading to a goal in all competitions this season, the joint-most of any Premier League goalkeeper alongside Tottenham Hotspur's Hugo Lloris.
In addition, concerns over the 32-year-old's ability to play out from the back has also been called into question, as Erik ten Hag searches for a shot-stopper comfortable with the ball at his feet.
Nevertheless, Ten Hag defended his widely-criticised number one on Sunday night and confirmed that he wants to see De Gea extend his contract at the Theatre of Dreams.
The Spaniard is currently due to become a free agent at the end of the season, and Man United are not prepared to activate an existing 12-month extension, which would keep him on his club-high £375,000 weekly wage.
Instead, the powers-that-be are insisting that De Gea must agree to a salary decrease of around £175,000 to stay on, taking his weekly pay down to £200,000, which he has so far shown no willingness to do.
Now, The Mirror claims that some members of the Red Devils' hierarchy are doubting whether De Gea should even be offered a new deal after all, despite Ten Hag publicly giving the green light to a renewal.
Man United are believed to have scouted a number of potential replacements for De Gea, including Brentford's David Raya, Dinamo Zagreb's Dominik Livakovic and Porto's Diogo Costa.
While contract talks continue to rumble on in the background, De Gea has insisted that he remains "very happy" in Manchester and expects negotiations to yield a positive solution.
The shot-stopper has kept a club-high 188 clean sheets in 540 games for Man United in all tournaments, overtaking Peter Schmeichel's previous record of 180 in February's EFL Cup final.
That 2-0 success over Newcastle United at Wembley saw De Gea win his eighth piece of silverware with Man United, having also won the Premier League, Europa League, FA Cup, three Community Shields and another EFL Cup in 2017.
A total of 540 appearances for the Red Devils is also the seventh-most in the club's history behind Ryan Giggs, Bobby Charlton, Paul Scholes, Bill Foulkes, Gary Neville and Wayne Rooney.
However, De Gea's mistake at the London Stadium has left Man United just one point clear of Liverpool in fourth place in the table, albeit with a game in hand on their Merseyside rivals.