United confirmed the Portuguese manager's exit following 14 months in charge after he lashed out at the board in the aftermath of a 1-1 draw with Leeds United at the weekend.
Mainoo, who was often in conflict with Amorim liked a social media post discussing the decision made by the board which sparked conversation online.
Mainoo must prove himself
The midfielder himself has not publicly commented on his former manager's sacking, but many suggest he will be delighted with the decision to Amorim go.
Speaking to casino.org, Owen has stated that Mainoo has to take his chance now that Amorim has gone if he is to establish his spot in the United first team.
"By the very fact that Amorim has gone, you would think that he's going to get a lot more opportunity to play, but that's where the positive for him ends in many ways
"Now it's down to Mainoo. It's all right blaming people, but of course, his time is now going to come and he's got to take it.
"He's got to take that opportunity because if the next manager doesn't play him and the next manager doesn't bring him on much, then at some point, a little bit like Marcus Rashford, those doubts might start to creep in.
"He'll be thinking, ‘Am I playing well? Am I listening to the information I'm getting? Am I disciplined? Am I all of these things?’
"Right now, he will be one of the happiest people about, but now it's going to be squarely on his toes, and there's no hiding place or excuses.
"He's got to now prove that Amorim was wrong by not playing him as much. He's probably going to get that opportunity, so we'll see."
Amorim had insisted the midfielder would not be permitted to leave on loan during the January transfer window, describing him as "the future of Manchester United".
Now, as the January window is open, it is unclear whether the midfielder will be free to leave if he suggests a departure to interim manager Darren Fletcher.