phrase request - "Physician's writing" - "to scribble like a chicken with claw"

Is there any phrase for describing when someone writes extremally illegibly?

In Poland it's called "physician's script", or there's an idiom "pisać jak kura pazurem", which literally means "to scribble like a chicken with claw".

It's very popular in Poland. Well, at least I've heard it on every occasion.

Answer

The English equivalent is similar: chicken scratch.

This would be a noun phrase to describe the writing, not the person, though, so an example would be:

"I can't read a word of John's chicken scratch. Can you translate it for me?"