Thing is they wouldn't have any way to know on the spot, and there's no real danger of playing on in terms of further damage.
They would have gone in with a set idea of minutes they wanted into him for his preparation so if he can continue they want to get him there.
The alternative is you leave him off, he doesn't get the minutes and then you have the dilemma of whether or not he is right for round one, and also potentially expose him to a higher risk of soft tissue issues. If it turns out his wrist was just a knock then that is a very bad result.