MMA got me thinking...will workmans comp put the screws to me in the future?

I tore my pec while lifting weights and had surgery in May to repair it. I did this outside of work and therefore I have to use all my own sick, personal, and vacation time while I'm out of work. I work a security job which I sometimes have to break up fights and restrain people. Seeing I did this outside of work, this IS NOT a workmans comp case. My doctor said he will most likely clear me to return to work full duty in Sept. (4 months post surgery). He said by that time this will not easily retear when I have to get physical with somebody. Here's where I may find a problem...

Let's say when I go back to work (after being fully cleared by my doctor) that after 2,3, maybe 4 months...I get into with someone on the job and I reinjure this pectoral. Obvioulsy, I will than have to be out of work again, but this time I would be out on workmans comp and wouldn't have to use my own sick, personal, and vacation time while I'm out of work. My question is will workmans comp say "hey you may have reinjured this while on the job, but you initially injured it off duty while lifting weights...screw you, we aint payin you, use your own sick time!"

I asked my union president and he said that if my doctor clears me to go back to work full duty, technically, I have a clean bill of health, and even if I reinjure the very same injury, workmans comp HAS to pay me. He said worst case scenario, they may fight it and at first deny the claim, but eventually I would win a hearing thus them paying me what they owe me.

What do you guys think?