My friend was suspended for an inappropriate and unprofessional behaviour, because he got drunk on Christmas corporative dinner and said unpleasant words to his manager.

Now he is invited for disciplinary interview, and nearly sure he will be dismissed. 

Because for him it is a question of UK working visa, he wants to delay this interview as long as possible, to find another job.

What is his rights in this case?

Can he ‘get sick’? And if yes, that for how long?

Does he need a letter from GP?

Thank you in advance for your advice. 

And Merry Christmas!