Referee Samuel Barrott made the controversial decision to send United defender Matthijs de Ligt off the pitch in the first half's added time due to a persistent bleeding head wound.

While De Ligt was receiving treatment on the sidelines, Brentford's Ethan Pinnock managed to score from a corner while the hosts were a man down, leaving them incensed at Barrott's decision.

Footage from the tunnel revealed Fletcher arguing with fourth official Gavin Ward as he entered the tunnel at half-time, followed by 31-year-old Barrott and his assistants.

Ex-United midfielder Fletcher, whose son Jack was among Saturday's substitutes for the home team, now anxiously awaits to see if the incident will be included in Barrott's match report.

If it is, Fletcher may find himself facing disciplinary action from the FA for his foul-mouthed rant towards the match officials.

After full-time, Ten Hag explained the United staff's dismay over the controversial opener, which intensified the current sack pressure.

"We didn't know why the referee made one of our players, at a vital moment, go off the pitch because it was dry blood," the United boss said.

"So it had already happened. [It was] before a corner, for the critical moment, so it was strange.

"He is one of our best headers, maybe even our best header at the moment. They can benefit from it so we were frustrated."

Alejandro Garnacho and Rasmus Hojlund completed a comeback to ensure United's winless run didn't extend to six games.

He added: "Of course, we feel it was really injustice, and it wasn't right, the way they handled the situation, but we have to live with that, and I think we showed the right response.

"We put that as fuel and we showed a quick start to the second half. There was anger and we transferred that into quality. We wanted to do things right and we did, scoring two beautiful goals."