Official Government guidance on exercise says it should be limited to once a day and “you should not travel outside your local area”.
The park has been noticeably busy with families exercising and the PM is said to have been concerned by what he saw in the area.
A few hours after his cycle, Mr Johnson held a meeting with cabinet colleagues to discuss the current lockdown.
A source told the Standard the PM was exercising, adding: “But he did note how busy the park was and he commented on it at the meeting last night.
“He was concerned about if people were following the rules and was concerned after his cycle ride around the park.”
The Standard has asked 10 Downing Street whether the PM cycled to the park or was driven there in a vehicle for his bike ride. However, officials declined to clarify.
Some social media users have pointed out that there are green spaces closer to the PM’s home in Westminster where he could exercise.
Health Secretary Matt Hancock was asked during Monday’s Downing Street press conference if you were allowed to exercise seven miles away from your home.
He replied: “It is OK to go - if you went for a long walk - and ended up seven miles away from home. That is OK, but you should stay local.
"You should not go from one side of the country to another potentially taking the virus with you.
“Remember one in three people who have the virus don’t know they have it because they have no symptoms and yet still pass it on.”
He added: “It is OK to go for a long walk or a cycle ride or exercise – but stay local.”
Andy Slaughter, Labour MP for Hammersmith, said: “Once again it is do as I say not as I do from the Prime Minister. London has some of the highest infection rates in the country. Boris Johnson should be leading by example.”
It comes amid speculation that lockdown is set to get tougher with tightened face mask rules and limits on exercise.
Chief Medical Officer Chris Whitty today warned that the NHS is now at the “most dangerous time” in its history and appealed to people to obey the rules or risk spreading infections.
Meanwhile, the vaccinations minister told people not to sit on park benches to chat with friends amid mounting concern over rule-bending.
Nadhim Zahawi was asked on Times Radio if people should avoid sitting on park benches, and replied: “Don’t go out and sit or have that opportunity of social interaction, because you’re helping the virus and that’s what we want to avoid.”