12:18 PM PT -- Ronda said this "freak accident" happened on her first take of the day. She said a boat door jammed her finger and initially didn't think anything of it -- "I'm used to live audiences and never showing pain unless I'm supposed to" -- before realizing the danger she was really in.
After finishing her take, Ronda said she was rushed to the hospital where her bone and tendon was reattached to her finger with a plate and screws. She said, "I returned to filming the next day and finished my scenes before returning home to recover." And, get this ... Ronda says she had 50% range of motion back in 3 days ... calling it the mighty power of medicine.
It's nice to see she's still got her personality. She ended her Instagram post with, "And of course tune in to see how well I can act like my finger didn't just fall off in this upcoming season of @911onfox."
8:17 AM PT -- Check out this photo -- THIS INJURY IS NASTY!!!
Turns out, Ronda's injury was WAY worse than we first thought -- we're told Ronda injured TWO fingers in the incident, her middle finger and her ring finger.
The middle finger got the worst of it -- it was broken and her tendon was nearly severed. She also fractured the tip of her ring finger.
She was taken by ambulance to a San Diego hospital for treatment where we're told her middle finger was repaired with a bolt and screws.
The craziest part ... RONDA WENT BACK TO WORK THE NEXT DAY!
We're told Ronda plans to explain the whole thing on her website momentarily.
Ronda Rousey is so tough, she BROKE HER FINGER on the set of the "9-1-1" TV show -- BUT NEVER BROKE CHARACTER!!!
Ronda -- who plays an L.A. Fire Dept. badass on the show -- was shooting a scene in Mexico last week in which she was supposed to slam a door during a dramatic action moment.
But, as one source put it ... "She was a little over-exuberant and slammed the door on her finger."
We're told Ronda didn't wince, didn't complain, didn't mess up the scene ... instead, she continued to stay in character and finished the scene.
Only after the director yelled "cut," we're told, Ronda FINALLY acknowledged the injury -- saying, "Ow. You're not gonna like this!"
Ronda went to a doctor who diagnosed her with a broken finger -- which is NOTHING for the former UFC superstar.
She got a splint for her hand and went right back to work the next day, our sources tell us.