United have won the past three Premier League games, with Ferdinand accusing Amorim of risking his job with his stubbornness.
"I admire it to a certain extent," Ferdinand said on his personal podcast. "But, like I said, I think he is playing Russian Roulette with his job. I don't think he's changed drastically, he's just tweaked.
"That's what a lot of fans were asking for. Just tweak what you've got. Maybe don't be so much on the front foot, maybe be a bit more conservative at times when we haven't got the ball.
"You can't press, press, press for 90 minutes, unless you're an absolute beast of a team. PSG do it. This manager couldn't do that with this squad.
"That's just sometimes how the cookie crumbles. We might look back in six months and, say Man United finish in the Champions League or something like that, he'll probably sit there confidently and go, 'Well, if I did change, I probably would be out of a job because I have been doing things that are alien to me'."