Amorim remains under huge pressure at United after defeat at Brentford left the club sitting 14th on the Premier League table. With no European football this season, United were also bounced out of the Carabao Cup by Grimsby Town.
Asked if he can see a way back for Amorim, Parker told Tribalfootball.com: "In Ruben Amorim and what he's trying to do, no not now to be perfectly honest. It's been too long and it's not it's not going to work.
"It is disappointing that he's not willing even now just to put his hand up and just say... not even publicly... just to even come out and just change (his system).
"I'm surprised that he hasn't during the game and gone to a four (at the back) when he's losing. You can bring on another defender, but just change it to a 4-5-1 and just be compact, sit deep, and just say we're not going to get beat and counter-attack."
Amorim can play off the break
Parker believes Amorim does now have the players to play more off the break. But laments that the Portuguese doesn't appear willing to make the tactical adjustments.
He continued: "United fans love counter-attacking football. He hasn't got the... He wasn't equipped and blessed in the squad for players to do that. Maybe, however, now because of (Matheus) Cunha and because of (Bryan) Mbeumo and because he's got (Amad) Diallo with a little bit of pace and goal.
"(Benjamin) Sesko's got a bit of pace about him. He's got technique to hold the ball up, and you can get more players to join in there from midfield. That's what I look at. I'm no tactician, just common sense to me. So, to answer your question, no, I can't see it now (turning around)."
Parker added, "If it was to happen, you're looking for something to happen, which will just be incredible for him to hit the ground, playing his style with these players, and everyone going, 'we've got it all wrong, he's got it right'.
"It ain't going to happen now. The performances don't suggest it."
- Paul Parker was speaking with Tribalfootball via Casino.org, known for helping Brits find great online casinos