The former Tory MEP ignored Foreign Office guidance which says no one should travel unless it is essential.
Mr Johnson Snr told the Daily Mail he was in the country "on essential business" to ensure a property he rents out was "Covid-proof" before holidays restart.
His Prime Minister son was quizzed about the trip on LBC but replied: “I think you really ought to raise that with him.
“My view is that the overwhelming majority of the British people have understood what needs to be done.
“I’m not going get into details of family conversations.”
He was repeatedly asked by presenter Nick Ferrari for a comment on his father’s actions, but replied: “No.”
However, Transport Secretary Grant Shapps earlier defended the 79-year-old’s actions arguing that he had ignored travel “advice” but “not restrictions”.
The Secretary of State told Sky News: “As I say, it’s advice. Everyone can decide what to do with the advice. The important thing is quarantine is in place.”
Asked if the advice was optional, he replied: “Well, yeah, the clue is in the name. But the quarantine isn’t.”
Stanley shared photographs on his Instagram account on Wednesday, showing him arriving in Athens and at an airport in a mask.
Speaking from the balcony of his villa in northern Greece, he said: “We must get these air bridges set up as soon as possible. From what I've seen the arrival of the British will not be a danger to the Greeks because they're so careful here.”