“We have to fight in the next game.”
Worse could be to come as United travel to runaway Premier League leaders Liverpool on Monday NZT before facing Arsenal in the FA Cup third round.
Amorim has come under criticism for refusing to budge from his 3-4-3 formation since joining from Sporting Lisbon, where he won two Portuguese league titles.
The 39-year-old reacted to a disastrous start by replacing Joshua Zirkzee after just 33 minutes with Kobbie Mainoo.
United improved after the change, but the damage had already been done.
Amorim, though, was adamant that he will not change his ways, even if it ultimately costs him his job.
“You cannot go back, you have to continue to push,” he added.
“We’ve had four training (sessions) all together, I was (brought) here because of my idea and I will continue with my idea until the end.”