Ruben Amorim has said he's not expecting reinforcements to his squad in the January transfer window as he attempts to arrest Manchester United's worrying slide towards the relegation places.

Defeat to Newcastle at Old Trafford on Monday was United's fourth in a row in all competitions. It has left Amorim's team 14th in the table and just seven points off the drop zone.

One of the issues facing the Portuguese coach is a lack of players who fit his 3-4-3 system, but he's not expecting the club to spend money to fix it when the transfer window opens on Wednesday.

"We don't have that possibility in January," Amorim said. "You know the situation better than I [do]. It's not the case I am not arriving here and I can spend a lot of money, changing all the team. You know the situation so it's not a point to talk about it."

Sources have ESPN that any business United do in January will be dependent on players leaving. The club are open to both permanent transfers or loans and if money does become available a new left wing-back would be the priority.

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Amorim is already facing questions about whether he should adapt his system to the players he has available.

But the 39-year-old insists he will stick with 3-4-3 as he prepares for a daunting trip to Anfield to face league leaders Liverpool on Sunday.

"I have to sell my idea." he said. "If I change all the time it is going to be even worse. But I understand they have a lot of difficulties because they spent two years playing one way. You can feel it, I can feel it but I have to sell my idea, I don't have another one."

Amorim, who has played 3-4-3 throughout his managerial career, also rejected the suggestion that reverting back to 4-3-3 -- the system preferred by his predecessor Erik ten Hag -- would fix some of the issues facing his team.

"When you have a change of coach, especially in this type of club, it is because they were not winning," Amorim added.

"They play in the system they were bought for and were losing. So I am going to change to that system? This team was already in problems."