My thought is to show up for the first day because showing up makes an impression which can't be made by not showing up.
People generally recognize that random injuries happen & will heal, especially when they can SEE the injury.
They cannot see what doesn't show up.
I'm the kind of person who would show up at the appointed time and announce with a big smile, "Ain't that how life goes, want to make a good impression on my first day at a new job and here I had the dumb luck to get a sprained ankle. Anyway, here I am!"
And the employer, theoretically, thinks, "aw man, sorry about your bad luck, well, ya got here, that's a good thing, let's see what we got that you can do"
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"There are a thousand things that can happen when you go light a rocket engine, and only one of them is good."
Tom Mueller of SpaceX, in Air and Space, Jan. 2011