UFC fighter Rachael Ostovich's MMA fighter husband has been arrested for ATTEMPTED MURDER days after allegedly breaking his wife's face ... and he's still behind bars in a Honolulu jail.
TMZ Sports broke the story ... Ostovich -- who had to pull out of her scheduled January fight with Paige VanZant -- was hospitalized this weekend with serious injuries -- including a broken orbital bone -- after her husband allegedly assaulted her during an argument at their home.
Cops in Honolulu opened a domestic violence investigation earlier this week ... and now police officials tell us 27-year-old Arnold Berdon -- Ostovich's husband and father of her child -- was arrested Tuesday evening on suspicion of 2nd degree attempted murder.
Berdon -- a fighter himself who holds a 7-2 record -- is still in custody at the Honolulu PD main station.
He has not yet appeared before a judge ... where bail could be set.
If he is released ... Rachael's husband won't be allowed to contact Ostovich -- 'cause she got a restraining order ... barring contact.
For his part ... a family member of Arnold told us he intends to vigorously dispute in court any allegations he assaulted his wife.
If convicted, Berdon could face life in prison with the possibility of parole.