There is a requirement for TDs to declare any gift worth more than €650 from a friend -- unless they can show that it would have no influence on their decision-making.
A member of the Dail committee which oversees the system has called on Mr Adams to officially declare the fact that Mr Flynn paid for his private US operation.
"The way things are now, if you get a donation of any kind, including medical expenses, you'd be better off to declare it from the off," he said.
But Sinn Fein has said that Mr Adams did not include the payment for the medical procedure in his Dail declaration of interests for 2012, which was filed last month. It is due to be published alongside those of other TDs in the coming months.
Mr Adams confirmed last weekend that Mr Flynn had paid the bill for his "surgical procedure" for a non-cancerous prostate problem in New York last summer -- at an estimated cost of $30,000.
"I didn't pay for it. A very, very good friend of mine, a man called Bill Flynn, very kindly paid for it. I haven't told anybody that before," he told RTE's 'Marian Finucane Show'.
Sinn Fein could not be contacted for comment about whether Mr Adams was going to change his Dail declaration.