It is usual for a pre-op appointment to establish the home circumstances and whether any help is needed. Then, after the op, the physio usually checks whether the patient can get up and down the stairs before they are discharged.
If you think he is being discharged too soon when you see what he can do on Monday, then you will have to make it clear to the ward staff that he lives alone and will not be able to manage - and that he cannot go home till care is in place.
But, as others have pointed out, as long as he can manage, he is safer away from hospital bugs.
There will be drugs he needs to take when he is discharged and he needs to be able to manage taking those at the right dosage and the right time.
I was in for 5 days because of some post-op problems; and I needed lots of help at home afterwards too.