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.

A US judge said the plaintiffs could pursue claims that the film unit of the Sony corporation had been negligent.
The plaintiffs are seeking to hold Sony liable for not bolstering security after previous breaches.
"We are pleased that the court has properly recognised the harm to Sony's employees," said lawyer Michael Sobol.
Many Sony employees had their personal details made public in 2014 when a group calling itself Guardians of Peace leaked data from the studio's computers.
The attack was described as an act of revenge motivated by Sony's release of The Interview, a comedy about an assassination attempt on North Korea's leader.
The nine plaintiffs claim Sony Pictures Entertainment violated a California confidentiality law by spurning security measures to stop the theft of employees' salary and health data, Social Security numbers and other sensitive information.
Without ruling on their action's merits, US District Judge Gary Klausner said Sony had created a "special relationship" with its employees by requiring them to provide personal information to be eligible for salaries and benefits.
The former workers said Sony's negligence caused them economic harm and that the hack had been "an epic nightmare, much better suited to a cinematic thriller than to real life".
The Interview, starring James Franco and Seth Rogen as journalists recruited by the CIA to assassinate Kim Jong-un, was initially withdrawn from cinemas but was later made available online.

Contact with flight MH370, carrying 239 people, was lost en route from Kuala Lumpur to Beijing. Despite an extensive search no trace has ever been found.
The trial system enables planes to be tracked every 15 minutes, an increase on the current 30 to 40 minutes.
It uses technology already installed on most long-haul jets.
The system is expected to increase the tracking rate to five minutes or less if there is any deviation from a plane's expected route.
Australian Transport Minister Warren Truss said the new system was a "world first". But he stressed the new technology would not necessarily have solved the mystery of MH370.
"It would have been very difficult, one would imagine, without knowing what precisely occurred in the case of MH370, to have intervened from outside," he said.
"But at least it would have tracked the aircraft to within 15 minutes."
Airservices Australia Chairman Angus Houston, who helped lead the search for MH370, agreed it was "no silver bullet".
"But it is an important step in delivering immediate improvements to the way we currently track aircraft while more comprehensive solutions are developed," he added.
The trial will begin in the Australian city of Brisbane, before being extended to Indonesia and Malaysia.
Investigators searching for MH370 are focusing on an area of the Indian Ocean off the coast of western Australia.
Former Australian Prime Minister Tony Abbott has said his decision to award Prince Philip a knighthood was "injudicious".
[NEXT_CONCEPT]
Sony Pictures Entertainment has failed in an attempt to dismiss a legal action brought by nine ex-employees over the cyber hack that crippled the studio.
[NEXT_CONCEPT]
Australia, Indonesia and Malaysia are to trial a new method of tracking planes, almost a year after a Malaysia Airlines flight disappeared.