Tough budget settlements for the Welsh NHS have made it "exceptionally difficult" to deliver health services, top civil servants have said.
Welsh government senior management board members warned that without extra money "very significant options for change would need to be considered".
The Conservatives said the message of the "dangers" of "record-breaking" NHS cuts may "finally be getting through".
But ministers said they were already reviewing whether more cash was needed.
Health Minister Mark Drakeford announced earlier this month the review would take place over the summer with Finance Minister Jane Hutt.
The Welsh government's senior management board, chaired by Permanent Secretary Derek Jones, is made up of top civil servants in Wales - the directors general for each department, as well as a number of non-executive directors from outside the organisation.
Minutes of a meeting at its headquarters in Cathays Park, Cardiff, in March record that: "The board noted the challenges facing the NHS and the mitigating actions.
"Members commented that the delivery of the current range of NHS services would be exceptionally difficult within a flat cash settlement and in the absence of additional revenue resources very significant options for change would need to be considered."
The minutes record that the Welsh government's Director General for Health, David Sissling, was present at the meeting.
The NHS in Wales is estimated to be facing a cash shortage of nearly £404m for the current financial year - compared to £330m last year.
In recent years, Wales' seven local health boards have received only small percentage increases in their budgets, while the Wales Audit Office (WAO) has said inflation and demand costs facing the service will rise more than 4% every year for the next three years.
The WAO has also warned that over recent years NHS Wales has faced tougher financial settlements than its counterparts in other parts of the UK.
For example, the Welsh government's total budget for health this year is £5.495bn, with next year's projected to be £5.489bn - a decrease of around 0.09%. Last year it was £5.492bn.
Changes to the health service have proved highly controversial over the past 12 months, with protest groups springing up across Wales to campaign against local reorganisation plans.
The Conservatives have called for an inquiry into failings of the NHS in Wales similar to the Keogh review of NHS trusts in England.
Shadow Health Minister Darren Millar AM said: "Welsh Conservatives have repeatedly warned of the dangers of Labour's record-breaking NHS budget cuts.
"This meeting - and the finance review that has come about as a result - are further proof that the message may finally be getting through to a stubborn Labour government.
"Even government officials can now see the extensive damage that has been caused by Labour's failure to protect the health budget.
"It is a shame that is has taken this - and a series of catastrophic failings - to convince ministers that something must be done.
"It is now vital that this summer's NHS finance review amounts to more than a simple tea-room chat between the ministers for finance and health."
On Tuesday Mr Drakeford told BBC Wales ministers were reviewing whether more money was required, albeit in the context of huge pressure on all public spending.
"There are new pressures that the NHS is funding and we will want to see that the NHS has the money it needs to meet those new demands," he said.
Mr Drakeford also responded to a recent barrage of negative headlines for the health service about governance issues, cancelled operations and even patients dying while on waiting lists.
He said: "The real story about the NHS in Wales is that it goes on, day in, day out, providing treatment for people right across Wales which were unimaginable even five or 10 years ago.
"Of course there are pressures, of course there are problems, of course there are things we want to do better, but the real story is not the story of things going wrong.
"The real story is of a service that provides more treatment for more people more quickly than it has ever done before, and it does that because of the dedication of the people who work in it, and because of the investment we continue to provide to the NHS even in the times when money is very scarce."