degenerative disc disease operation question

I've previously had 2 surgeries on the same disc (L4) in the past 8 years.  After the 2nd surgery, I was informed that I have degenerative disc disease. I've dealt this this pain again for the last 3 years and finally the pain has gotten so bad that I'm talking to a surgeon again.  He's telling me that even though he can see that the disc is in bad shape, that BCBS probably won't let him proceed with a fusion operation unless I've done a certain amount of physical theropy.  Is this true?  If the Dr suggest spinal fusion, will it be denied until I've gone through physical theropy even though it's been determined that I have DDD?