Speaking on the Gary Neville Podcast, the ex-England defender said: "I thought it would get better when Ruben Amorim came in. I thought the enthusiasm and the new system, I thought they'd buy into it the players, and we'd see a bounce. We've seen the absolute opposite. It's got a lot worse and that's surprising.
"But there's going to be a lot more pain towards the end of the season and it is going to be damaging. They're obviously going to stick with Ruben Amorim, but the more you lose, the more difficult it is to convince the players of the idea. The idea that he talked about in the early days. You need the players to buy into it, but if they lose with it, and they keep getting criticised, the spotlight comes on them more and the fans are leaving unhappy."
He added: "You can't keep losing. It will depress the thoughts of the players, to the point whereby they'll lose faith with the idea. It'll damage the start of next season. He has to do something. He can't change his approach because he's died in a ditch on it. And rightly so. I think he's lost more games at Manchester United since he's come than he lost in the last 75 at Sporting."