As PP said, it's up to the person/organization accepting the excuse. A similar conversation just came up with my high school sister who has jokingly asked me for an excuse out of gym class. I don't know their gym policy, but she said the school did make a policy that only MD/DO physicals would be accepted to start playing a school sport.
From a different perspective, I work as a school-based PT. I generally make those calls, with one exception. If a physician has written an order to refrain from activity, we require the physician's follow up order to release them. I respect that they're looking at test results and imaging that I haven't seen.
