"He knows the whole country is doing its bit and he wants to help. But it's complicated as he was originally grounded from the job so that he could become a senior working royal."
The source said his role as a royal is currently even more important afer Charles tested positive for coronavirus.
Charles, Camilla, the Queen and Prince Philip are all in self-isolation - while Meghan and Harry have started their new life in Canada after stepping down.
Suggestions of William's return come after the death toll from the virus in the UK rose to 1,408.
On a visit to a 111 NHS call centre earlier this month, William spoke about his desire to help out in the NHS.
He also became patron of the London Air Ambulance Charity earlier this month.
London Ambulance Service boss Garrett Emmerson said: "As he knows well, we have an air ambulance service here in London.
"I know he would be welcome there any time."
The NHS is facing growing pressure as the government warns of a "critical peak moment" approaching.
Around 20,000 former NHS staff have been re-recruited to help during the pandemic and a quarter of a million people have volunteered their services.
A huge conference centre in east London has also been transformed into a hopistal.
The building usually operates as ExCel London, an exhibition and convention centre.
Initially 500 beds equipped with ventilators and oxygen will be used to treat the seriously ill.
Construction has been carried out by NHS staff, along with engineers from the British army.
On the defence force website, a statement from Defence Secretary Ben Wallace said military planners and engineers had been working "hand in hand" with the NHS to support their development of the building.
"The Armed Forces have already been distributing personal protective equipment (PPE) to meet the increased demand and we stand ready to assist further in any capacity needed."
Prince William reportedly wants to return as an air ambulance pilot to help "do his bit" in the fight against coronavirus, a source said.
The Duke, 37, spent two years with the flying medics before stepping down from service in 2017.
Now William has reportedly expressed an interest in returning to the frontline during the biggest health crisis the UK has experienced in a generation.
However, as one of the few senior royals currently still working - a source says he worries his duties could prevent him from doing so.
They told the Sun : "William has been seriously considering returning as an air ambulance pilot to help in the current pandemic.