"We’ve received really distressed messages from our patients saying, ‘please, please, please do not send me to Christmas island. I was there five years ago, I was there six years ago, I don’t want to go back'," Dr Rufener told SBS News.
"This is a place that caused fear, anxiety and worry in them five or six years ago and to put them back into that situation when they’re acutely ill quite frankly is cruel.
"People who have experienced trauma, when they’re re-exposed to a traumatic situation often their symptoms worsen."
The government says it will spend about $1 billion upgrading the facilities on Christmas Island.
Few ever sent back
Attorney-General Christian Porter on Thursday raised fears the Medevac legislation would be a "one-way ticket" for asylum seekers off Manus Island and Nauru, despite only a handful of asylum seekers being sent back under the existing medical transfer system.
Mr Porter said he's received legal advice that the new law removes the government's power to return asylum seekers to offshore detention once they have completed their treatment in Australia.
However, the government rarely uses the existing power under the immigration act.
Home Affairs officials told a Senate estimates hearing on Monday that 1,246 asylum seekers have come to Australia for medical treatment and only 282 have been returned.
Nearly 900 remain in Australia with just one person sent back last year.
Labor's immigration spokesperson Shayne Neumann said the new laws had not changed the returns system.
Dr Rufener said it is unrealistic to send people with serious mental health issues back to indefinite offshore detention.
"If a person is transferred to Australia for temporary medical treatment, we will return them to Manus or Nauru once doctors advise they have completed medical treatment," he said in a statement.
Impact of new laws uncertain
MSF has just begun a telehealth service for asylum seekers on Nauru after its doctors were kicked out of the country five months ago.
Dr Rufener said it was unclear what impact new laws passed by the Nauruan government banning overseas remote assessments would have on their services.
She said MSF was yet to refer any patients for transfer under the new Medevac laws.
"How that’s going to work with the changes in Nauru law, or changes that happen in Australia, I don’t know."
Dr Rufener urged the debate on border security to focus on the health of asylum seekers.
Politicians have 'flicked the fear switch'
Former Race Discrimination Commissioner Tim Soutphommasane said the "alarmist rhetoric" from the government about the Medevac bill was a concerning sign of things to come.
Source: SBS News/Rosemary Bolger
"In this election year, there is every indication that the Coalition government has flicked the switch to fear," Professor Soutphommasane is expected to say in a speech on Thursday night.
He warns that comments from government frontbenchers referring to asylum seekers as "rapists, murderers and paedophiles" gives the impression that "Armageddon awaits vulnerable Australians".
Border security is expected to dominate the campaign and the government's strong rejection of the Medevac bill has already delivered it a boost in the polls.
"Might the fearmongering get worse between now and the election later this year? Could this be just a preview of a race politics put on steroids?"