He needs representation.
No matter how smart he is; how familiar with the job, or having a perfect previous employment record;, he needs a representative - ideally from a union, or a lawyer.
If he wants any chance of keeping his job.
The employer needs to go through due process if they are intending to sack him.
The first step in that is a disciplinary hearing.
I'm no lawyer, but I would have thought he needs written notice of at least a week, so that he has time to get a witness or rrepresentative to help him during the hearing.
Apart from giving legal/moral and practical help, a witness or supporter means it is much more difficult for the employer to claim he agreed to something, or admitted something when he did not.
Employers do this.
Once it is in the official record of the hearing, it becomes 'true' even if it did not happen. He can dispute it, but there wil be at least two employer representatives in the room, and they can assert he said anything, unless he also has a supporter.