Workers' Party (WP) chief Low Thia Khiang said there were no talks between his party and the Singapore Democratic Party (SDP) that led to the latter's last-minute withdrawal from the Punggol East by-election.
But he said he was not surprised by the turn of events though he declined to elaborate.
While mingling with supporters at the nomination centre, he told The Straits Times: "I've been in politics long enough."
Mr Low also said the WP respects the right of all parties to contest any constituencies and that the party remains focused on supporting its candidate Lee Li Lian.
Separately, WP Aljunied GRC MP Pritam Singh said he has not started looking for a new legislative assistant.
He will need one to replace the Workers' Party candidate Lee Li Lian if she's elected in the Punggol East by-election. "It's a happy problem that I'll look into," Mr Singh told ST.
He also sang praises of Ms Lee, who has served as his legislative assistant since 2011, as someone who can connect easily to people.
The WP is up against three other candidates: Dr Koh Poh Koon of the PAP, Mr Kenneth Jeyaretnam of the Reform Party and Mr Desmond Lim of the Singapore Democratic Alliance.
It contested in the ward against the PAP and SDA in the 2011 general election and garnered 41 per cent of the vote.