I'm getting Rhinoplasty and I'm a MMA fighter.

Definitely best to retire from fighting/contact sports before having a rhinoplasty otherwise you risk undoing all the good work done

The terms rhinoplasty and MMA do not often mix until your fighting career has ended.  If a rhinoplasty is being performed for functional and cosmetic reasons, the nose loses about 15% of its original strength - meaning, if you get hit in the nose again, you will be more likely to fracture it.  My recommendation is to wait until you are done fighting; then, undergo a rhinoplasty for the first - and last - time.

Thanks for your question. When I see athletes who play contact sports about nasal surgery, I always counsel them that less is more. If you can't breathe and your nasal bones are messed up, you can have them straightened without burning any bridges for the future. However, if you want to have a definitive surgery that will fix your breathing and improve your nose's looks, I'd absolutely counsel you to WAIT until after you're done with MMA. The risk of subsequent fracture is too great and the fix would be much harder than it needs to be.