Michael Cohen claimed he was never reimbursed for the payment to Stormy Daniels in 2016 and neither the Trump Organisation nor Mr Trump's campaign team were involved.
Mr Cohen had arranged the payment to Daniels, whose real name is Stephanie Clifford, to keep her from publicly discussing the alleged sexual encounter in 2006 during the presidential campaign, according to the Wall Street Journal.
In a statement to the New York Times, Mr Cohen said: "Neither the Trump Organisation nor the Trump campaign was a party to the transaction with Ms Clifford, and neither reimbursed me for the payment, either directly or indirectly.
"The payment to Ms Clifford was lawful, and was not a campaign contribution or a campaign expenditure by anyone."
Mr Cohen declined to say whether Mr Trump was aware of the payment or why it had been paid, the New York Times reported.
It comes after the watchdog group Common Cause filed a federal complaint in January about the payout, arguing it may have violated campaign finance rules.
Ms Clifford believes she is now free to discuss her alleged sexual encounter with Mr Trump.
Her manager says the adult film actress believes Mr Trump's lawyer invalidated a non-disclosure agreement by publicly discussing the payment.
Ms Clifford claimed in a 2011 interview that she and Mr Trump had a sexual encounter after meeting at a golf tournament in Nevada in 2006 - a year after he got married to Melania.
She was reportedly in talks to discuss Mr Trump with US media ahead of the 2016 US election.
Mr Cohen has previously said Mr Trump "vehemently denies" the alleged affair, while Daniels has since said in a statement that it never occurred.
But during an appearance on Jimmy Kimmel Live in January, the actress appeared to disown the statement, saying she did not know where it came from and the signature did not look like hers.
