That's a stupid thing to as you do get regular checkups, and eye screening etc for realI had an idiot of a supervisor who used his Type 1 Diabetes to blag time off. He was an admin nightmare of weapons grade proportions. Anyway, one Friday he didn't come in and I didn't hear anything from him even though I chased.
He eventually texted me on the Sunday with an image of him in bed on a drip, with an explanation of why he didn't come to work.
I didn't really take much notice of the image, but on the Monday when he came in, it dawned on me. In the photo he was clean shaven, on the Monday, he had a sizable beard and had it for weeks.
He bluffed his way that it was an old photo and he had sent the wrong one etc.
So when I had had enough and was about to start proper performance management, he saw the writing on the wall and found another job (which he lasted less than 6 weeks in)
But then you have written evidence of appointments should it be questioned
The last time I was on a drip was due to a diabetic coma and it was a bit obvious when I got back to weeks later I still visibly looked ill
If he was ill enough to be on a drip he'd have been be able to provide something from his GP to back it up