Explosive details regarding the final weeks of Ruben Amorim’s tenure at Manchester United have emerged, with reports revealing that the Portuguese coach and defender Lisandro Martinez "squared up" to one another during a heated training ground confrontation in December. The Argentine World Cup winner reportedly confronted his manager in an "intense" manner over a lack of playing time, though the incident ultimately earned him the captain's armband.The autopsy of Amorim’s 14-month reign at Old Trafford is well underway following his dismissal on Monday, and stories from inside the Carrington dressing room are painting a picture of a manager who walked a fine line between charm and conflict. While the former Sporting CP boss was generally well-liked by staff and fans for his charisma, his communication with the playing squad appears to have been the friction point that ultimately sparked tensions.According to a report from The Athletic, one of the most volatile flashpoints occurred just last month involving fan-favourite Martinez. The incident took place during a difficult run of fixtures in December, specifically around the time United faced Crystal Palace and West Ham.Tensions reportedly boiled over when Martinez, who had been restricted to substitute appearances against both Palace and West Ham, felt he was being unfairly overlooked for the starting XI. The defender, known as 'The Butcher' for his aggressive style of play, believed he was fully fit and ready to start, but Amorim continued to leave him on the bench.The disagreement culminated in a physical confrontation on the training pitches where the player and manager "squared up to each other." The exchange was described as "intense," with Martinez making his feelings known in no uncertain terms. In an era where player power often dictates that such outbursts lead to exile, the outcome of this row was surprisingly different.Looking for smarter football bets? Get expert previews, data-driven predictions & winning insights with GOAL Tips on Telegram. Join our growing community now!Rather than freezing Martinez out, Amorim appears to have responded positively to the challenge. The report suggests that the manager admired the fire and energy shown by the Argentine defender. While Martinez was still left out of the starting lineup immediately following the row, the exile was short-lived.By the time the Boxing Day fixture against Newcastle United rolled around, not only was Martinez reinstated to the starting XI, but he was also handed the captain’s armband. He retained the captaincy for Amorim’s final two games in charge, a clear signal that the manager respected the player's desire to fight for his place.This incident highlights a specific facet of Amorim's management style: he was willing to be challenged if it came from a place of competitive desire. However, this approach evidently did not work with every member of the squad.Add GOAL.com as a preferred source on Google to see more of our reportingWhile Martinez managed to turn a confrontation into a promotion, others were not so lucky. The report notes that while Amorim was "charming and generous" with regular staff and supporters, a section of the dressing room felt his communication left a lot to be desired.Players reportedly wanted better clarity on their roles and reasons for omission, something Martinez had to forcefully extract via a training ground argument. For others, the lack of dialogue festered, contributing to the disjointed performances that eventually cost Amorim his job.As United now search for their next permanent manager, the task will be to unify a squad that has seen both exiles and fights under the previous regime. Martinez, now established as a leader who isn't afraid to confront authority, will likely be a key pillar for whoever steps into the dugout next.