Will delaying start date get my job offer rescinded?

I am supposed to start a new job next Monday. I sustained a nerve injury and I cannot get into see the specialist until Monday. If I go to the appointment it means I will have to delay my start week because I would miss new hire orientation which is also on Monday. The company requires everyone start on Monday. I am afraid they will rescind my offer if I try to delay. How likely is it that my offer will get rescinded?

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