Andrew Lansley has called on GPs who are planning to take industrial action in a row over pensions to work an extra day to clear their backlog.
The Health Secretary has already expressed his disappointment over doctors' plans to take action on June 21 in protest at the Government's controversial pension reforms.
In a new letter to the British Medical Association (BMA), Mr Lansley says that GPs could catch up with missed work by working on Saturday June 23.
He told the chairman of the BMA council, Dr Hamish Meldrum, that the action "gains doctors nothing" and "will harm patients".
The union announced the day of action last month after it accused ministers of pressing ahead with "totally unjustified" increases to pension contributions, and a later retirement age for doctors even though a deal on pensions was agreed four years ago.
The BMA said that on June 21 all non-urgent work will be postponed. The union said that although the action will be disruptive, doctors will ensure patient safety is protected.
Doctors will see anyone who is ill, or who believes they are ill, on the day of action - but will not do paperwork.
Most doctors will be taking industrial action for the first time, with the last dispute almost 40 years ago.
Mr Lansley said that up to 1.25 million GP appointments would have to be pushed into the days and weeks following the action.
This includes 140,000 appointments for children up to 14 as well as 400,000 appointments for pensioners.
He said up to 30,000 operations could be cancelled including 1,350 cataract surgeries and 700 hip or knee replacements.
In his letter to Mr Meldrum, Mr Lansley writes: "As GPs are self-employed, I would also ask you to ask your members who are GPs that they consider working on Saturday 23 June to clear the backlog of appointments they will have created by their action on 21 June.
"As you know, the action GPs will take could potentially displace up to 1.25 million appointment bookings in primary care into the days and weeks following your strike - including appointments for some 140,000 children.
"GPs understand better than anyone today's routine appointments can become tomorrow's emergencies.
"I would like to reiterate once again, which I hope you now increasingly recognise, that the public will not understand or sympathise with the action doctors are taking.
"Industrial action gains doctors nothing, will harm patients, and leaves you isolated from the other major NHS unions. Do think again."
Responding to the letter, Dr Meldrum told Mr Lansley that the decision to take action "was not taken lightly".
He added: "Tens of thousands of grassroots doctors feel so strongly that the changes to their pension scheme are unfair and unnecessary that they have decided to take industrial action - the first time in almost 40 years.
"Doctors know the industrial action they take cannot be the same industrial action taken by any other work force.
"This is why doctors will be in their usual workplaces and patient safety remains their top priority."