Of course that's what "they" will say. But:
1 - It's not up to "their" doctor to make that decision.
2 - It's not up to the employer to make that decision.
It's up to your husband to go into work and say "This is too painful, I'm going home." And then just do it no matter what the employer threatens.
Then he can call the insurance company and say "I can't work anymore, too painful, send me the forms for the weekly benefits."
Then he can go to his own doctor.
Then he can hire a WC attorney if he has to.