I think it would be worse not to tell the boss. What if you try to keep on working and you are unable to do something because of it? Then you tell the boss. Maybe put him in a jam because he was counting on you to complete a job and now he has to pull someone from somewhere else to cover. You just made two headaches for him. I've always gone with "honesty is the best policy".
I do agree with "honesty is the best policy" and I think I'm going to tell my dispatcher, they are the ones who dole out the work, then see what happens.
I worked today with my cast on and had no issues, even pulled out a blower motor and rolled around in a crawl space.