A 26-year-old female amateur MMA fighter died Sunday morning ... just one day after collapsing in the ring following a brutal loss at an event in England.
The Hampshire Police Dept. confirmed they were called to Southampton General Hospital around 1 AM on Sunday to respond to a woman who suffered a life-threatening brain injury.
The woman, Saeideh Aletaha, had competed at the Fast & Furious Fight series event at Central Hall in Southampton, England on Saturday ... and reportedly collapsed in the ring.
According to local reports, an ambulance was called to the venue around 9 PM and Aletaha was rushed to the hospital in "a serious and life-threatening condition."
Cops say Aletaha died at the hospital Sunday morning -- and they're now investigating her death.
Organizers behind the F&FFS event posted a statement early Monday morning essentially saying Aletaha knew what she signed up for ...
"All competitors get in [the ring] prepared that they may be injured and this is something not expected to happen 99.9% of the time."
FFS organizers say they had a full medical team on-site -- with doctors, paramedics and an ambulance -- along with an "experienced team of staff with numerous first aiders."
Exile Gym, where Aletaha trained, posted a tribute to the fighter ... saying, "Saeideh Aletaha was a lovely character with a beautiful soul. Her dedication to the sport was 110% travelling miles every day just to train."
"She found her place with us just a few months ago but has become apart of the family and will be sorely missed."