Ex-employee faking injury

The employee is trying to commit fraud and we know it. He is trying to sue my dad for an accident that occurred. He was hit on the back from something on my dad's boat but denied my dad's request to see a doctor. He remained working for 7 days then came back to sue him. He claims that he's injured and can never work again, but my dads friends who own other boats have claimed that he's been down to the dock to buy shrimp/fish to resale under the table and is able to carry heavy boxes. No one is willing to testify because they are scared of him. What actions should we take besides hiring an attorney (and what kind)? What should an private investigator look for? How else can we prove he's not injured? The doctors record shows he came in for a car accident but his lawyer argued that the clinic has changed owners and paper could have been lost. What should we do?