Ruben Amorim's emotional and inconsistent behaviour was a key part of Manchester United's decision to sack him, Sky Sports News understands.
United wanted stability and structure when they appointed him, which he brought in the early part of his reign, but a refusal to adapt and evolve his system led to the breakdown in confidence in the head coach.
Amorim had a scheduled meeting with director of football Jason Wilcox on Friday, where the team's tactical approach was discussed in detail. Sky Sports News has been told United's bosses felt Amorim's response at that meeting was very negative and emotional.
This was not a sacking based around Amorim's preference for 3-4-3. Rather, it was on the basis of what United saw as the head coach's refusal to adapt his tactics to differing circumstances and the evolution of the team.
It was not the result of differences in opinion over the January transfer window, although the two sides did not see eye to eye on whether to strengthen now.
Sources point out that the club has spent approximately £250m on new signings since Amorim arrived, and he knew the plan was always to strengthen the central midfield in the summer.
The attempt to sign Antoine Semenyo from Bournemouth was opportunistic, because he has been a long-term target of the club, but that would never be allowed to jeopardise the summer plans.
United's bosses feel the team are still well-placed to secure a European place, and so because of the negativity of the head coach, particularly with repeated emotional statements in the media, they felt his position had become untenable.
The overriding feeling was that, whilst the bosses believe in this group of players, they didn't feel the head coach shared their optimism.
The agreement when Amorim joined was to have a plan for stability and then evolve the team and tactics, but United feel he failed to implement that.
After a poor run of results, the heated meeting with Jason Wilcox, and Amorim's repeatedly negative comments to the media, change was inevitable.
United didn't want to change head coach again, but felt they had no choice.
Amorim's damning stats in charge at Man Utd
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What now for Amorim?
Amorim is likely to head back to Portugal in the coming days, Sky Sports News understands.
Amorim is understood to feel he was not getting the backing of the club hierarchy and is frustrated by what has happened.
Amorim is understood to have wanted to sign an experienced Premier League striker in this window.