Emeritus Senior Minister Goh Chok Tong yesterday described Dr Tan Cheng Bock's recent decision to announce his bid for the presidency as a "calculated political gambit" that is open to interpretation.
Mr Goh added that by making his statement as a Constitutional Commission is reviewing the process, Dr Tan runs the risk of being seen as trying to influence the panel's work and politicising the system.
His comments came a day after Dr Tan, a former People's Action Party MP, said he was making a second bid for the presidency.
Dr Tan lost the 2011 presidential election to President Tony Tan Keng Yam by 7,382 votes, comprising 0.35 percentage point, in a four-way race. The next election must be held by August next year.
Mr Goh told The Sunday Times: "His move was a calculated political gambit and, of course, it is open to many interpretations or even misinterpretations. One could interpret his move as coming from someone who is ambitious, as making a move to be president, or it could be to discourage others from coming in.
"Last time, there were four candidates and he nearly won, (he) lost by a small margin. So if you can discourage others from coming in, it's a straight fight, then you will have a better chance."
The 2011 presidential election was also contested by Mr Tan Jee Say and Mr Tan Kin Lian.
Mr Goh said a second view could be that Dr Tan is "rallying the ground to support him". He added: "Once the ground supports him, it may make it more difficult, he thinks, for the Constitutional Commission to come up with criteria that may disqualify him. This is speculative, of course."
A nine-member commission led by Chief Justice Sundaresh Menon is reviewing the eligibility criteria for candidates, the role of the Council of Presidential Advisers, and steps to ensure minority candidates can be elected from time to time.
Mr Goh said what Prime Minister Lee Hsien Loong was seeking through the review was "correct".
"I know how the Government thinks, we plan ahead to ensure there will be a stable, fair and contestable system that will stand Singapore in good stead. And the system must enable good candidates to contest for president," he said.
"But the commission is still reviewing the process. By coming out now and risking being misunderstood that you are trying to influence the commission's working, in a way, he has been politicising the process."
He also said that he was not surprised by Dr Tan's announcement.
"Indeed, he is an old friend," said Mr Goh. "I've known him for over 55 years. What he did was in keeping with his character. Once he has decided to do something, (he) will do all he can to achieve that goal."
Asked if Mr Tan had consulted him about the move, Mr Goh said: "In the past, we would have spoken to one another. But after the last presidential election, he was and will be on his own.
"We are still very good friends, still go out with each other, but I will not try to influence him... I will just wish him good luck."
Mr Goh was at a film screening in Marine Terrace. Nine short films about Marine Parade and its history - produced by Temasek Polytechnic students over four months - were screened for residents.