MANCHESTER, England -- There has been a simmering discontent at Manchester United for a while now, but at Old Trafford on Monday night the dial was turned up to near mutiny in a loss to Newcastle United.

With just 30 minutes gone and Man United already 2-0 down, Joshua Zirkzee was substituted by head coach Ruben Amorim. Any of the 11 players could have been replaced -- they were all that bad in a shocking first half hour -- but it was Zirkzee who bore the brunt from the irate supporters in the stands.

When Zirkzee's number went up, there were loud cheers around the stadium. The Dutchman, only signed from Bologna in the summer, grabbed his coat and jogged down the tunnel to scattered jeers. He emerged again moments later to take his place on the bench. When the half-time whistle blew, there were boos from all four sides of Old Trafford. There were more at full-time, although by then a large number of the fans who turned up had long since decided it was time to go home.

It's now four straight defeats for Man United and six in their past eight games. For the first time since the 1978-79 season, they've lost three consecutive league games at Old Trafford. Three Premier League defeats in a row mean they will start 2025 in 14th, just seven points above the drop zone.

Man United's woes have reached the point where Amorim is being asked about the possibility of relegation.

"It is really hard on everybody and you can feel it," Amorim said after the 2-0 loss. "We show some improvement in the first games especially against [Manchester] City and Tottenham but we are losing that because of the lack of training and belief after so many losses. It is a really tough moment for everybody.

"It is a bit embarrassing to be Manchester United coach and lose a lot of games. I think our club needs a shock and we have to understand that."

There was little shock that Newcastle were by far the better team and deserved to win their first league game at Old Trafford for more than a decade. Man United managed to calm some of the anger with a more competent second-half performance, but by then the damage had already been done.

Alexander Isak scored for the sixth game in a row after just four minutes to make it 1-0. Before 20 minutes had elapsed, Joelinton made it 2-0. It could have been much worse. Isak had a goal ruled out through offside, and Sandro Tonali hit the post when he should have scored.

Only then did Zirkzee come off. He was replaced by Kobbie Mainoo and Man United finally turned up to play. By half-time, Newcastle had taken 11 shots at André Onana's goal. As the game drifted towards its conclusion, the travelling Newcastle fans sang, "You're getting sacked in the morning," at Amorim.

After the initial optimism of his arrival to replace Erik ten Hag in November, it has been a bruising December for the Portuguese coach with Premier League defeats to Arsenal, Nottingham Forest, Bournemouth, Wolves and now Newcastle. Man United haven't lost five league games in a calendar month since 1962.

Throw in the Carabao Cup defeat to Tottenham and it's six losses in all competitions, a low point not seen since September 1930. For the first time in more than 100 years, a Manchester United manager has lost five of their first eight league games.

The question, though, is whether it's Amorim or the players who should be shouldering the blame. For now, Amorim is refusing to criticise his squad despite further evidence week after week that the majority are not good enough.

He's routinely peppered with questions about his 3-4-3 system and whether he will -- eventually -- have to adapt. But his formation had nothing to do with Isak having a free header six yards out after getting in between Harry Maguire and Lisandro Martínez to head past Onana.

It had nothing to do with Joelinton bulldozing Martinez out of the way to head in the second. It had nothing to do with all the missed tackles and missed passes.

"I am responsible," said Amorim. "I don't like to arrive here and make excuses. I think people are tired of excuses in this club. I never watch a coach winning games by not protecting the players. What I have to say to the players I say in the dressing room. "I have to sell my idea. If I change all the time it is going to be even worse. It is a very difficult moment and we have to fight for the next game and to also have a performance."

Writing in his programme notes ahead of the game, Amorim said he had "no doubt" that the run of miserable form "will not last forever." It is, however, unlikely to end immediately with United scheduled to visit runaway leaders Liverpool next weekend.

Defeat at Anfield would send Amorim and his players deeper into the mire. The anger is already deepening, the mood worsening by the day.

Even for a club that has made a habit of lurching from crisis to crisis, United are reaching new levels of despair.