It's probably best you did tell them it happened off-site (I.e. maybe intensive yard work or moving large appliances in the house). Because if any injury occurs on the jobsite, before you can start work again, they will probably send you to a company doctor (not yours) for a physical and drug test.

I had a co-worker who had a filing cabinet fall on her, she was rushed to the hospital. But before she could start work in the office again, she had to go to the company doctor and get a clearance from him.