Sprent Dabwido, who had his passport confiscated in August, just as he was set to depart for Australia to see a cardiologist, collapsed at Nauru hospital on Wednesday.
Mr Dabwido, who had served as an MP for 12 years, including two as president, is one of a number of now former MPs who had opposed the actions of the government and this is believed to have led to the cancellation of his passport.
A colleague Mathew Batsiua, who is another former MP, said the government must relent and let Mr Dabwido get the treatment he needs.
"Apart from being a public servant in very high office, he is first and foremost a Nauruan, and he should be treated equally by the Government," he said.
"He is entitled for certain programmes that he can access, so he can receive his medical treatment - he should be given those and not be targeted and victimised because of political differences in the past.
Photo: UN Photo/J Carrier