The firefight erupted on October 15 while Boonyarit and other Thai soldiers were stationed on disputed land near the ancient Preah Vihear temple.
Thailand and Cambodia have claimed ownership to Preah Vihear.
Public Health Ministry permanent secretary Dr Prat Boonyawongvirot yesterday said Boonyarit was now on lifesupport system. "He is unconscious and shows no response to pain," Prat said. Even after surgery, Boonyarit's brain is still swollen.
The volunteer ranger is being treated at the Ubon Ratchathanibased Sappasitprasong Hospital where
Dr Monchai Wiwattanasittipong said Boonyarit was under close medical supervision.
According to Prat, three other soldiers injured in the same incident were now in a safe condition.