In my opening scene we meet DR. CHIMERA.  During that scene it is obvious he is known to the main character.  Then there is a flashback to their actual meeting.   The short action description I've included is when the main character passes the Dr. but is UNaware at that time who he is.  

Scattered clapping.  
Nash passes the fight physician, a middle aged man in a white shirt and khakis sitting in the front row.  
It’s Dr. Chimera.  
He looks Nash over then loses interest.

Nash enters the cage, continues to loosen up in his corner.     

My question is, anything I should Capitalize?  FIGHT PHYSICIAN??  or DR.CHIMERA?  Audience and reader know who that is but Nash doesn't at that moment.

Hard to tell, but stick with the basics imho, of only capping the character when he's first introduced (on screen) to us, the reader.