Sarath Fonseka's health had deteriorated since he was held at the naval headquarters in Colombo after his arrest on February 8 and was in need of urgent medical attention, said his wife, Anoma Fonseka.
"I suspect that the government is insisting that he is not suffering from any ailment to deny him specialist treatment and thereby ensure his natural death in custody," she said in a statement.
Anoma Fonseka said her husband needed specialised care since suffering injuries in an April 2006 suicide assassination attempt blamed on Tamil Tiger rebels, whom he eventually crushed in May last year as army chief.
Following concerns raised by Sarath Fonseka's political allies, the military had denied earlier that the general's health was failing and said a medical examination had found nothing wrong.
"A naval doctor and another specialist examined General Fonseka on Monday morning," the military said in a statement, adding that the doctors had not noticed any health problems with the former army