Actually I think it is a breach of confidentiality.
Discretion being the name of the game. The practice manager 'overheard' a conversation. The practice manager should not then have taken this information to someone else.
If she/he had concerns then go to the people she had overheard it from and explain concerns, but you don't go to someone else. That's called gossip. (Eh, Doctor X thinks so and so might have...aids, syphilis, ...whatever) It's not done.
That is, of course, if the situation would require the intervention of the practice manager - perhaps the GPs concerned would rather have spoken to the nurse/OP first?
There's too little discretion in these situations today - I'm a patient who has been on the receiving end and it's no fun and it causes a lot of trouble.
With regard to affecting the patient's ability to do the job - well, there are surgeons with Parkinson's and we don't know when the GP noticed the tremor, it could have been in a coffee break.
Golden rule - they should speak to the person they have the concerns about 'first' and give them the opportunity to explain if they should wish and/or if the situation necessitates it.