Amorim had looked downbeat on Friday when discussing potential transfers, and the Portuguese coach grew visibly irritated when pressed about whether he still had the board's confidence.
The 40-year-old cut off reporters with a sharp rebuke about "selective information" before launching into an emphatic defence of his position.
"I came here to be the manager of Manchester United, not to be the coach of Manchester United, and that is clear," a visibly frustrated Amorim said after the 1-1 draw at Leeds United.
"I know that my name is not (Thomas) Tuchel, it's not (Antonio) Conte, it's not (Jose) Mourinho, but I'm the manager of Manchester United.
"It's going to be like this for 18 months or when the board decides to change."
Amorim made clear he has no intention of walking away from Old Trafford, repeatedly emphasising his managerial authority over simply coaching duties.
"So that was my point. I want to finish with that. I'm not going to quit," he added.
"I will do my job until another guy is coming here to replace me."
'I am the manager, not just the coach'
When pressed further about assurances regarding his ability to manage the team, Amorim doubled down on his stance.
"I just want to say that I'm going to be the manager of this team, not just the coach. And I was really clear on that," he said.
"And that is going to finish in 18 months, and then everyone is going to move on. That was the deal. That is my job, not to be a coach."
Amorim then took aim at external criticism, suggesting the club needed to change if it could not handle commentary from television pundits like former United player Gary Neville.
"If people cannot handle Gary Neville and the criticism of everything, we need to change the club," he said, before reiterating his core message.
"I just want to say that I came here to be the manager of Manchester United, not to be the coach. And every department - the scouting department, the sports director - needs to do their job.
"I will do mine for 18 months, and then we move on."
