He was an "unofficial backup" to Mr Png Eng Huat, the Workers' Party (WP) candidate for the Hougang by-election.
This was what party veteran Poh Lee Guan told reporters yesterday when asked why he had applied for a political donation certificate.
He was not at the nomination centre, but in a coffee shop nearby.
But WP leaders said his move caught them unawares. Secretary-general Low Thia Khiang said he was not told of Dr Poh's plan.
Political observer Eugene Tan said of Dr Poh: He's a party renegade who is out to gain attention, and that his actions had not only hurt his credibility, but undermined his party's standing at a critical time.