The move earlier this year sparked widespread public and political backlash with many questioning whether the British royal deserved Australia's top honour.
It came after Mr Abbot revived Australia's honours system last year.
The new cabinet under Malcolm Turnbull is set to review the honours system.
Mr Turnbull, the new prime minister, ousted Mr Abbott from power in an internal party challenge last month.
On 26 January - Australia's national day - Mr Abbott announced he had nominated Queen Elizabeth II's husband to receive the knighthood.
He had said then that the Duke of Edinburgh's life of "service and dedication" should be honoured. The Queen awarded the knighthood in April.
Asked on Thursday in an interview with radio station 3AW about his decision, Mr Abbott said: "Obviously it was an injudicious appointment."
Australia's honours system
The move was met with scorn from many among the Australian public, who questioned the Prince's contributions to Australia and pointed out that as a British royal he was a symbol of another country.
Some media outlets called it a "Knightmare", opposition leader Bill Shorten called it "anachronistic", and Mr Abbott faced criticism from within his own Liberal party.
Mr Turnbull, who used to chair Australia's republican movement, had previously defended the honours system's revival in 2014, noting that most republics have an honours system and an order of knighthood.
But he is now said to be in favour of abolishing the system, according to Australian media reports.
Former Australian Prime Minister Tony Abbott has said his decision to award Prince Philip a knighthood was "injudicious".