Lawmakers have urged Chief Executive Tung Chee-hwa to explain the abrupt departure of his top aide to allay public suspicion.
Lam Woon-kwong resigned as director of the chief executive's office with immediate effect on Thursday.
He said he quit because he did not wish to tarnish his boss's image and denied any link to the blocking of Taipei Mayor Ma Ying-jeou's proposed visit to Hong Kong. Mr Ma has been refused a visa.
Mr Lam resigned after Sudden Weekly printed photographs of him at the Grand Hyatt Hotel in Tokyo with barrister Po Wing-kay.
Democratic Party chairman Lee Wing-tat said he would urge Mr Tung to explain Mr Lam's sudden departure during questions in the Legislative Council on Thursday.
Fellow democrat Cheung Man-kwong said it sounded strange that Mr Tung had let his top aide go in a matter of hours. 'He urged unpopular ministers like [former financial secretary] Antony Leung Kam-chung and [former security secretary] Regina Ip Lau Suk-yee to stay after they tendered resignations,' Mr Cheung said.
Mr Lee, who spoke to Mr Lam hours before he resigned on Thursday, said he told the aide that barring Mr Ma from visiting Hong Kong could cause political trouble.
