Manchester United and Chelsea are the biggest teams this season but they have performed worst and time. The manager of United has worked with Manchester United for several seasons but he has not been able to give significant performances for Manchester United so far. So this season may be Manchester United's last season for the current manager. On the other hand we can see that Chelsea spend a lot of money on their club every season and in the past few seasons they have regularly changed their manager duties from their club and maybe this season they will also change their club manager duties. If Chelsea had a skilled manager in charge instead of changing managers every season then maybe this team would have a better chance of success.
Actually, these two teams are having the weakest performance among the top teams in English premier league this season. However, I will differ from your opinion on Manchester united manager. Quite alright, I know this season is probably among one of the worse season for Manchester united but Erik ten Hang gave his best to the team first season of his arrival but the performance is getting worse as he progresses but despite this challenges, I don't think Manchester united is ready to pathway with the tactician as there is no sign of such from the management. It's the fans making such calls but I'm not sure the management will listen.
Chelsea on the other hand, their case is just like the more you look, the less you see. They are quick to pathway with their managers despite that it is not making any positive impact. Infact, since the termination of Thomas Tuchel appointment, their case has been like from frying pan to fire as the new manager appoint perform worse than his predecessor. They have been spending huge money on average players with no impact on the club for like three consecutive seasons now. Their problem is yet to be identified, thus, no one is able to proffer solution.
Since the manager is not able to bring success for the team even after serving for a few seasons, then the manager must take full responsibility for this. But if the club did not show financial problems, in order to improve the performance of the team, the manager could add the players he needed to the club as soon as the transfer window opened. Every manager tries to give maximum for the team but even after giving maximum in some cases some mistakes remain in the strategy of some managers due to which such changes in team performance can be noticed. If United feel that a change of manager can put them in a better position then they could look at a change of manager. As we approach the end of the season, if Manchester United decide on this, it will probably be at the end of the season whether they will change managers or continue with the previous manager.