Stacey Mitchell, a spokeswoman for the office, said it could be several days before the official cause is determined.
In 1998, American Doug Dedge died after being knocked out in an unregulated fight in the Ukraine.
A mixed martial arts fan Web site said Vasquez was the first such fighter to die from an injury incurred or aggravated while competing in a regulated bout, though no official statistics were available.
A call to the Texas Department of Licensing and Regulation, which sanctioned the fight, was not immediately returned Monday.
Vasquez was hospitalized after he was knocked out by Vince Libardi of San Antonio in the third round of a fight at the Renegades Extreme Fighting show. Immediately following the knockout, he lost consciousness and suffered a seizure.
Saul Soliz, the Renegades promoter, has been staging professional and amateur shows in the state since 2000 and had the necessary license to stage the event. Soliz did not immediately return a call Monday from The Associated Press.
Vasquez had been in intensive care at St. Joseph Medical Center before being transferred to a hospice last Monday. Vasquez suffered a massive stroke while hospitalized.
Comments attributed to Vasquez's wife Sandra on the mixed martial arts forum www.txmma.com indicated he was in a medically induced coma and had undergone two surgeries to remove blood clots in his brain. Vasquez was required to be medically cleared to fight, as are all combat sports bouts sanctioned by the Texas Department of Licensing and Regulation.
Vasquez is survived by his wife and a son.
