Ruben Amorim and Man United centre-half Lisandro Martinez reportedly squared up to each other during an intense training session just weeks before the Portuguese manager's sacking.
The 40-year-old was axed by the hierarchy at Old Trafford on Monday morning after a difficult 14 months at the club.
Daily Mail Sport understands that United's director of football Jason Wilcox made the decision to remove Amorim from his post as early as Friday, two days before the 1-1 draw at Elland Road.
It's understood the verdict followed an explosive meeting between Wilcox and Amorim late last week which prompted a furious reaction from the coach.
But it's now been revealed that tensions in the camp at Carrington had been brewing for some time before Amorim's dismissal.
The former Sporting Lisbon boss was embroiled in a heated confrontation with Martinez after the Argentinian's return from injury early in December, according to a report in The Athletic.
It came in the period when the Red Devils faced Crystal Palace at Selhurst Park and West Ham United at Old Trafford. 27-year-old Martinez is thought to have been left frustrated after being left on the bench when he thought he was fit to start, and confronted Amorim.
This led to the pair squaring up to each other on the training ground, with Martinez reportedly making his point in a manner described as 'intense'.
Amorim had indeed fallen out with a number of the Red Devils' most high-profile players during a little more than a year at the club.
After exiling Marcus Rashford, Jadon Sancho, Antony and Tyrell Malacia to his 'bomb squad', rumours of a rift between the Portuguese and Kobbie Mainoo were rife this season amid the Englishman's lack of game-time.
Mainoo was expected to leave Old Trafford on a temporary basis this month, though the departure of Amorim is likely to mean he now stays put.
According to sources, in his meeting with Wilcox on Friday, Amorim was told that United’s squad were good enough to earn trust and that they were capable of playing more attacking football.
The Red Devils director of football is also thought to have urged the coach to consider reverting back to the 4-2-3-1 formation which earned his side three points against Newcastle United on Boxing Day, though Amorim reportedly questioned how he was supposed to get results with a raft of first-team players sidelined.
It would appear the message the hierarchy at Old Trafford were trying to convey failed to hit home, with Amorim ultimately dismissed less than 24 hours after drawing with Leeds United.
He was informed of his fate early on Monday morning and seen later in the day looking jubilant while enjoying a stroll with his wife in the Cheshire frost.
A statement announcing Amorim's departure read: ‘Ruben Amorim has departed his role as head coach of Manchester United.
‘Ruben was appointed in November 2024 and led the team to a UEFA Europa League Final in Bilbao in May.
‘With Manchester United sitting sixth in the Premier League, the club’s leadership has reluctantly made the decision that it is the right time to make a change. This will give the team the best opportunity of the highest possible Premier League finish.
‘The club would like to thank Ruben for his contribution to the club and wishes him well for the future. Darren Fletcher will take charge of the team against Burnley on Wednesday.’
The Portuguese boss arrived at United in November 2024 from Sporting Lisbon but his poor record has seen him become a figure of mockery, topped when footage emerged of him using coaching magnets in the dugout during United's defeat by Grimsby Town in the second round of the Carabao Cup in August.
Former United midfielder and current Under-18s coach Darren Fletcher has been installed as caretaker manager for Wednesday’s trip to Burnley.