Brandon Williams was not quick enough on social media after he was caught out for posting a photo of Liverpool fans celebrating as he marked the collapse of the European Super League.
The 20-year-old looked to mark news that fan protests had helped ruin plans for a breakaway league but Williams' photo of celebrating fans was of United's bitter rivals Liverpool.
Alongside the caption 'To you all, everyone is equal' Williams uploaded a photo of Liverpool's open-top trophy parade for winning the 2005 UEFA Champions League to his Instagram.
He quickly spotted his gaffe and deleted the original post before replacing with a near-identical one, this time of Manchester United fans lining the street to celebrate.
But Liverpool fans were quick to spot the mistake and they were not ready to let the young full-back off.
'He's googled football parade and picked the first one,' one Liverpool fan wrote.
'Liverpool's biggest fan,' another wrote.
One United fan was left asking: 'How could you mess up as badly as this?'
Many of Williams' team-mates were quick to voice their opinions on social media before it emerged the plans had been ruined by a series of clubs getting cold feet following media and supporter backlash.
Captain Harry Maguire posted a photo of United supporters celebrating on Wednesday morning, captioning it: 'Let's all stay UNITED.'
United's players were unhappy at the owners' desire to form part of this 15-team cartel of teams looking to make a closed-shop competition.
As exclusively revealed by Sportsmail, executive vice-chairman Ed Woodward, who resigned on Tuesday night, held an emergency video conference call with the players from his Mayfair office on Monday after news of the breakaway venture broke over the weekend.
Captain Harry Maguire challenged Woodward and was not the only player to voice his displeasure, with others in the dressing room following suit.
Some had raised the prospect of refusing to play in the ESL should the club take part, and Bruno Fernandes, Marcus Rashford and Luke Shaw subsequently posted their opposition to the project on social media.
'Dreams can't be bought,' Fernandes put on Instagram.
Shaw penned an open letter to supporters while Rashford recalled a famous quote from iconic United boss Sir Matt Busby.