Ive been in a similar situation once. A few years back, I joined a new Advertising agency on a new big fat contract Just after I joined, my boss (who was the CEO) and I began to have huge conflict. I was great at the job but our personalities clashed. Within a few months, he decided he wanted me out. His problem was that I was excellent at my job and also had a 6 month notice period in my contract. His cheapest and most face saving way was to humiliate me into resigning.
He took away my authority and power, publicly ridiculed me in board meetings and ignored me in every other situation. As an already a seasoned professional, I knew the score and refused to be intimated I also had my lawyer write him a letter, cc-ing the global HQ. He quickly paid up my contract and I left.
But despite getting 6 months of pay and gardening leave I hated the situation and it left behind some emotional damage. ... I became very depressed and lost self confidence as I was stuck at home with nothing to do as it took me 12 months to find a new suitable position (my post count on redcafe rapidly increased!). That required some expensive counselling to solve. Likewise, it left a gaping hole in my CV that is still awkward to explain. I was headhunted into this firm: they lured me away from my existing employer and promised me riches and benefits to join them. The company did not belong to the CEO, he was an employee just like me, and he should have worked out any personality issues during interview stages. It was not my fault that they decided to want me and hire me!
You already know all of this. The fact that BFS is a footballer, or that he earns £200k per week has nothing to do with morality and legality. It was Manchester United's responsibility to assess BFS's fitness issues before he joined. And we should also had done some medium term recruitment planning. I know that many transfers don't work out, but that can never be the fault of the employee. The club need to work out fitness issues and then find ways to motivate its employee's. If the employee does not deliver, then sanction them with contracted penalties or HR assessment tools.
I have no issue in Mourinho deciding that BFS is not useful for his Manchester United. But if you want him to leave the club. Do it legally. Do it morally. Do it nicely. We don't seem to be doing that and Im very disappointed by that. I would not want to be tarred like that again.