The passenger should be mobile enough to handle the exit door and get out. Wearing a boot and needing crutches is not usually compatible with this.

If I saw this, I would discreetly (but directly) suggest to the cabin crew that they re-check the person in seat XX for exit row suitability and mention crutches, boots, etc. If they decided it was OK then that's their decision to make, but I would be wanting to ensure they have checked the situation in detail.

This has (nearly) happened to me once; I boarded early to an exit row, and part way through boarding a very frail-looking elderly passenger came to sit down in the exit row - who did not look physically capable of handling the exit row, or even a small hand bag. I was half way through heading to the nearest cabin crew member making "ah, I need your attention" hand motions and I met them half way, as they had already seen the problem and were making a beeline for the passenger. The passenger was discreetly ushered to sit in the row ahead, and I complimented the crew member later on "their good handling of the potential safety issue at the exit row during boarding".