An Australian academic and human rights activist who has been detained in the Philippines remains in limbo at Manila airport after being "blacklisted" on what he insists are trumped up charges.
Professor Gill Boehringer remains at Manila's international airport after being denied entry into the country when he arrived on a flight from China on Wednesday local time.
The government said it banned Prof Boehringer - who is originally from the United States - because he participated in a rally in November 2015 in violation of an order "prohibiting foreigners from engaging in political activities in the Philippines".
But his lawyer, Maria Sol Taule, has told AAP the 84-year-old wasn't even in the country at the time.
She is negotiating with immigration officials to allow him to stay in Manila until he has medical tests. Having the blacklisting lifted could take weeks, she added.
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"His legs are today very swollen and red and he's in pain," Ms Sol Taule said on Friday.
Prof Boehringer told AAP he remains in the custody of airline security staff and has not been allowed to leave the airport.
"I missed the (Friday) 8.30am flight so now we have to wait and see if the airline will let me leave later today," he said via a scratchy phone line.
The human rights activist said the airliner won't allow him to fly without first obtaining a clearance from a medical specialist outside the airport.
Geneve Rivera-Reyes from advocacy group Health Action for Human Rights examined Prof Boehringer and said he was suffering from deep vein thrombosis and cellulitis on both legs.
She agreed it was "not safe" for him to travel again without a medical clearance.
The NSW man, who is married to a Filipino woman, told Reuters he joined a fact-finding mission this year about indigenous people in Mindanao and the immigration bureau's accusation he previously joined protests was "trumped up".
"This is part of the government's campaign to keep foreigners away from what they're doing ... the injustices, the killings, the disappearances," he said.
