United are into next week's Europa League final, but sit just two places above the relegation zone.
"I think he (Amorim) looks around the dressing room and thinks 'If I could wave a magic wand, in the next five years at least 50 per cent of this team wouldn't be here'," Ferdinand said on his podcast, Rio Presents. "Because they're not good enough and they're not right for the way he wants to play.
"I look at him and think that he needs, minimum, two good windows of getting rid of the ones he doesn't require but also getting in players that he really needs."
He added: "There has to be a lot of things to go right for us to make a dramatic turn on this. He's coaching the turn to understand what he wants, which has led to him getting terrible results in the Premier League consistently.
"He needs to recruit dynamic athletes. I don't want no mavericks, or players that are frilly and can do pirouettes. No, no, people that can run past and over people as well."