Manchester United management can decide to keep the manager or fire him after considering how Manchester United performed under their manager last season. After taking charge of Manchester United team last season, the manager could not bring any player to the club but this season Manchester United has brought three new players to the club so Manchester United should have confidence in this manager for the entire season. If Manchester United manager fails to bring his team to a good position this season then the decision can be taken to remove this manager. But if the management decides to remove this manager now then it will definitely be an injustice to this manager.
Yeah, Manchester United shouldn't even think of firing him even though he brings nothing back home at the end of this season. Manchester United management needs to think of long term management, were the manager is given enough time to assemble his team and work with them without interference from them the management, I just think they need to stop this hiring and firing.
If Manchester United were to fire Amorim now, it would certainly be unfair. Last season, Amorim didn't coach from the start, so he wasn't involved in the transfer market like he is now, where he contributes to bringing in new players. So, it would clearly be unfair for Manchester United to fire Amorim now, as it's still early in the season. However, if Manchester United's performance worsens towards the end of the season, it would be reasonable for them to fire him.
In my opinion, looking at the first match of the season, Manchester United lost 1-0 against Arsenal, with Manchester United controlling much of the ball. I think this is a positive sign for Manchester United, as Arsenal is certainly a strong team in the Premier League. I personally hope Amorim is given time, as it's certainly not easy to build a team to progress. However, I'm confident Amorim will prove to everyone that he can help Manchester United bounce back and finish this season better than the previous one.