An elderly Australian professor has been living in Manila's international airport for the past week after he was denied entry into the Philippines.

Human rights activist Gill Boehringer was barred from entering the country after being placed on the Philippine Bureau of Immigration's blacklist.

The 84-year-old US-born academic, who is married to a Filipino woman, has not left the airport's international zone since he arrived on a flight from China on August 8.

The NSW professor says he was ordered on Monday afternoon to board a flight back to Guangzhou but his lawyer later confirmed the airline had refused to take him.

Australian professor Gill Boehringer (pictured) was barred from entering the Philippines after being placed on the Philippine Bureau of Immigration's blacklist

'Airlines will not board him without a medical certificate that he is fit to travel,' his lawyer Maria Sol Taule told AAP late on Monday.

Prof Boehringer has said the Philippines government incorrectly believes he participated in a rally three years ago.

Ms Sol Taule wants a medical expert from outside the airport to check her client but said BI has denied her client's latest application to stay in the country on medical grounds.

'We all agree that my "vital signs' are normal", the professor posted online on Monday.

'But what only the bureau fails to understand (or care about) is that you cannot predict that a person is fit to travel and not in danger from a deep vein thrombosis - which I have previously suffered - and nearly died from with a blood clot in my lung.'

The bureau said it was not detaining the Australian professor.

The 84-year-old US-born academic, who is married to a Filipino woman, has not left the airport's international zone since he arrived on a flight from China on August 8

It said he was instead in the custody of his airline because he had not been allowed entry to the Philippines.

Prof Boehringer said there was no basis for his exclusion from the Philippines.

Geneve Rivera-Reyes from advocacy group Health Action for Human Rights examined Prof Boehringer after he arrived in the Philippines and said he was suffering from deep vein thrombosis and cellulitis in both legs.

She agreed it was 'not safe' for him to travel again without a medical clearance.

The government claims it banned Prof Boehringer because his participation in a November 2015 rally violated an order 'prohibiting foreigners from engaging in political activities in the Philippines'.