Wendy Williams Says No to Replacement Hosts During Medical Hiatus

There's only one person capable of hosting "The Wendy Williams Show," even if she's sidelined due to illness ... and God help you, if you suggest otherwise!

We got Wendy Williams Tuesday afternoon outside her NYC studio right after she announced she's been diagnosed with Graves' diseases and needs to take time off. She had a nice farewell message for her fans, but her tone changed dramatically when we raised the possibility of a ... guest host?

Remember, doctors recommended Wendy take 3 weeks of vacation, stat -- so it seemed like a reasonable question.

Let's just say Wendy did NOT see things the way our photog did!