Mainoo came through the ranks at Old Trafford and was handed his debut by Erik ten Hag. He immediately shone and by the end of his debut season scored a goal in the FA Cup final as United shocked Manchester City at Wembley.
He went on to play for England as they made the final of Euro 2024, but since Ten Hag was replaced by Amorim his stock has fallen and his minutes have decreased. Mainoo failed to even get off the bench in the first two games and has since had to make do with substitute cameos.
Amorim has taken to starting Casemiro, whose future at the club has previously been questioned, ahead of him despite the Brazilian being into his 30s. Bruno Fernandes is also being played in a deeper role, which doesn't suit his qualities, ahead of Mainoo.
Parker maintains the matter must be personal as he told MyBettingSites: "We also have to ask why Mainoo hasn't been used in that midfield. Somewhere along the line because I've been looking at it, it has to be personal. It has to be personal and the truth has to be told somewhere. He doesn't like him or he doesn't like him as a player. It doesn't make any sense at all."
Despite Mainoo's meteoric rise at Manchester there has been talk of him being moved on, in part motivated by the PSR benefits of selling an academy player. He would still command a hefty fee but United have a famed history of backing their young talent and Parker has warned against selling him, especially given what he produced early on.
He said: "It would cause big problems if they allow Mainoo to go because he's a local boy. But it's not just about that, it's about what he's achieved in a short space of time and he hasn't been given the time and the respect."
Amorim has been questioned on his use of Mainoo but has been open about the improvement he wants to see in his game. "I believe a lot in Kobbie but some of you think that Kobbie Mainoo is already done. I think he can do so much better. He can improve in a lot," he said.
Mainoo is also competing with the likes of Manuel Ugarte, who is another player struggling for minutes under Amorim. It was also well documented that those on the red side of Manchester wanted to sign a No 6 to go into the middle of the park, leading to their interest in Carlos Baleba.
United's style under Amorim, which he's refused to veer from, requires legs in midfield and that has been cited as an issue with the current starting line-up in the early weeks of the season.