Outspoken liver expert and medical professor Lai Ching-lung will not have his part-time contract renewed by the University of Hong Kong, sources say.

Some see it as the university's move to purge politically outspoken scholars like 73-year-old Lai.

But HKU said the retirement age for all its staff is 60, adding that decisions on appointments are based on academic achievements and the university's needs.

The rejection of Lai's contract renewal is apparently made by the university's selection and promotion committee, even though its faculty of medicine planned to promote Lai to emeritus professor.

Sources suggested the contract denial had to do with Lai showing up at a booth to support a strike by hospital workers calling for all boundaries with the mainland to be closed at the onset of the coronavirus outbreak - even though he had not gone on strike himself.

It was also related to Lai having openly slammed the government for not closing all boundaries a few times, sources said, adding that "his outspoken behavior got on the nerves of university management."

The university declined to comment on whether Lai's contract renewal had been rejected.

"The university has stringent and impartial due procedures in handling human resource matters, and will not comment on individual cases," a spokesman said.

"Under the current procedures, the deliberation process of emeritus professorship normally will only begin near to the professor's retirement date."

Arisina Ma Chung-yee, president of the Hong Kong Public Doctors' Association, called on the university to publicly address why it would veto Lai's new contract.

"One won't think it is because Lai's academic achievements don't measure up," she said. "If that's the reason, it is extremely strange and beyond comprehension."

Ma said that the latest news about Lai was reminiscent of the 2015 vice-chancellor selection controversy at the university, during which Johannes Chan Man-mun -then the dean of the law faculty - could not take up the post of vice-chancellor following alleged political intervention as Chan was deemed to be a pro-democratic figure.

Lai has spent more than half a decade teaching at HKU and has had his full-time contract renewed at least three times since 2013, even though the university requires all staff to retire at the age of 60.

But in 2019, HKU offered him a two-year part-time contract when he was 70, which is due to expire on May 31.

In October, HKU also vetoed a new contract for Covid-19 control expert Keiji Fukuda, who will step down by the end of the year.

Lai Ching-Lung, center, backing the strike last February.

HKU to end outspoken expert's contract