Veera's relatives had taken doctors from Bangkok Hospital in Phnom Penh to treat him at high cost, Somchai said.
He asked how the government could help Veera, who is coordinator of the Thai Patriots Network, adding that the father of Cambodian Prime Minister Hun Sen was currently having cancer treatment in Thailand.
"The Thai government should ask the Cambodians to take care of him as a Thai citizen, not as their government's enemy," Somchai said.
Veera and his secretary Ratree Pipattanapaiboon are detained in Cambodia's Prey Sar Prison. They were sentenced to eight and six years in jail respectively for spying.