“Toxic”: this is the damning characterisation of Bruno Fernandes from one highly placed Manchester United source after the captain’s incendiary betrayal of Michael Carrick.

There has surely never been a greater anti-leadership act in United’s storied history than Fernandes questioning the man who trusts him to unify the dressing room and execute his on-field plan. The Portuguese has proved this faith wrong at the precise moment he was required to step up and exude a defiant togetherness.

Nothing could be more dysfunctional than civil war between United’s head coach and captain, featuring Carrick biting back at Fernandes for questioning his tactics as matters hit a new low in the aftermath of Wednesday’s pathetic 4-1 loss to Como. A litmus test for any leader comes when the storm arrives. At the Giuseppe Sinigaglia Stadium, Fernandes failed miserably, as he squealed about “the staff” deciding the best tactic was not to press Cesc Fàbregas’s bright, emerging team.

For “staff” read Carrick because he decides strategy and bears responsibility for performance. Fernandes is Carrick’s on-field proxy, so his behaviour is the dictionary definition of betrayal. Whether his conduct leads to disciplinary action in the way Lisandro Martínez’s calling out of Jason Wilcox did seems a greyer area.

Discussing tactics may be more within Fernandes’s remit, as captain, than a defender suggesting the director of football’s recruitment failed. Provided there is no damage to the team. But even if Fernandes issues an apology, some acts are irreversible. There is a case for Carrick to strip the 32-year-old of the captaincy and appoint someone such as Harry Maguire or Youri Tielemans.

Carrick is expected to hold his traditional pre-game media conference on Friday afternoon and be in charge for Bournemouth’s visit on Sunday, so when the team is announced whether Fernandes has the armband will intrigue. Could he even drop the playmaker? Whatever the decision, Fernandes can have zero excuse for his Como outburst.

Last week Fernandes witnessed how Martínez’s criticism of Wilcox became an extra headache for Carrick, whose sole focus should have been on arresting the direst start to a campaign since 1986. Instead Carrick had to thrash out the most prudent line of action – Martínez is understood to have been fined – then field questions about the episode from the media.

Yet still Fernandes rounded on Carrick after one of United’s poorest displays in continental competition. It was a performance the player was part of, having been on the field until Carrick removed him on 67 minutes. Being replaced by Joshua Zirkzee, who United tried to offload in the last window, shows how ineffective Fernandes was, first as a false 9, then, after the interval, in his favoured No 10 berth.

Fernandes’s comments indicate he is seriously disaffected with team strategy and his role within this. But is there, too, a frustration at still being at the club as his prime years begin to expire? This is a footballer who voiced disquiet last December, during a jarring interview with Canal 11, the Portuguese Football Federation‑owned channel, at “hurt” caused by United’s desire to sell him.

Fernandes was asked whether there had been an offer from Paris Saint-Germain or Real Madrid. He said: “Nowadays, the issue of loyalty is no longer seen the way it used to be. I could have left in the last window and would have earned a lot more. At one point I was going to leave and I would have won many trophies that season. I decided to stay not only for family reasons but because I genuinely like the club. The conversation with the coach [Ruben Amorim] also made me stay.

“But from the club’s side, I felt: ‘If you go, it’s not really that bad for us.’ More than hurting, it makes me sad, because I’m a player they have nothing to criticise me for.”

Now the club, and specifically Carrick, do feel seriously let down by Fernandes. But, it is also relevant to ask how Fernandes (and Martínez) have come to feel so at ease with going off-message.

These are highly remunerated employees. Their job is to play and maintain a united front – whatever happens – and for Carrick to allow a culture of entitlement to fester shows up a serious faultline in his management. For now, Carrick and Fernandes limp on – just like the team.

It will be some act for Carrick to save his job – even victory over Bournemouth may not do so – and for Fernandes to rehabilitate himself, before the head coach and fans. But this is football, a world that can be unpredictable and illogical.

The measure, though, of the debacle at Como, and the wider malaise at the club, can be found in Fàbregas’s post-victory words in which he bemoaned allowing Zirkzee’s added-time strike for United.

“I regret the last 10 minutes because I was the one who told the team to slow down the tempo because there’s another match [Sassuolo on Saturday] and at 4-0 we could manage things a little,” he said. “Their goal hurt me because we dropped our intensity and dropped our defensive block, but it was my fault.”

How Carrick wishes this was what he had to contend with – rather than a mutinous captain and a ship that seems to be sinking deeper on every matchday.