Dr Tan Cheng Bock, who lost in the 2011 Presidential Election, looks set to announce tomorrow a possible second bid for the presidency.

The former People's Action Party (PAP) MP for Ayer Rajah from 1980 to 2006 lost the 2011 election to President Tony Tan Keng Yam by 7,382 votes - or 0.35 percentage point - in a four-way contest.

Dr Tan Cheng Bock, 75, wrote in a Facebook post yesterday: "At the last Presidential Election in 2011, some 738,000 Singaporeans voted for me. Many of my friends and supporters have asked if I intend to contest in the forthcoming Presidential Election in 2017.

"I owe them an answer. This Friday, I shall let Singaporeans know of my intention," he said.

He declined to elaborate on this when asked by The Straits Times yesterday if he was planning to launch his bid for the presidency, but word on the ground is that he is likely to do so.

Dr Tan plans to hold a press conference at 10.30am at the MHC Asia Healthcare in Commonwealth. His wife Cecilia is chairman of the healthcare company.

The next presidential election must be held by August next year.

Dr Tan has remained in the public eye since 2011 and attended rallies by the PAP as well as several opposition parties during last year's general election.

Some opposition politicians as well as grassroots leaders from his old ward also attended a gathering at his house during Chinese New Year last month.

Political observer Derek da Cunha said on Facebook that the timing of Dr Tan's announcement is probably of significance, taking place amid a review of the presidency.

He wrote: "Will Dr Tan say that he would like to contest the next election as long as he meets the eligibility criteria, and that as he met the criteria back in 2011, that he should be permitted to re-contest in 2017?"

Dr Tan's post comes amid an ongoing review of the elected presidency by a nine-member Constitutional Commission chaired by Chief Justice Sundaresh Menon.

The review will focus on the criteria for who is eligible to stand for the election, provisions to ensure people from Singapore's minority communities have fair and adequate opportunity to be elected president, and refinements to the role and make-up of the Council of Presidential Advisers.

Several of Dr Tan's supporters, in comments on social media, see the review as an attempt to disqualify him from running for president.

The 2011 election was also contested by Mr Tan Jee Say and Mr Tan Kin Lian. Mr Tan Jee Say said last Saturday that he did not rule out standing in the next presidential election if he qualifies.