Ahead of the April 29 election, FAS general-secretary Winston Lee says Hougang United boss Bill Ng was aware that a S$500,000 donation was for AFF.
A 2015 donation of S$500,000 to the AFF came directly from Football Association of Singapore, says a statement on the ASEAN body's official website.
Singapore moved up four spots in the latest FIFA rankings, but failed to bridge the gap on neigbours Malaysia, who rose by the same margin.
"I had never thought about quitting. But I can't accept this [criticism] ... I made the right decision," says outgoing Thai coach Kiatisuk Senamuang.
After 3-0 and 4-0 defeats in their last two 2018 AFC World Cup qualifiers, Kiatisuk Senamuang sensationally quit as Thailand head coach on Friday.
The 2018 AFF Suzuki Cup will be contested by 10 nations after a decision by the Asean Football Federation to add two teams for future editions.