Prof Marcus Longley predicts tough choices and unpopular decisions in 2017 about the future shape of hospitals.
There have been long-term concerns that some specialist hospital services are spread too thinly on too many sites.
Prof Longley said smaller budgets and recruitment problems would see some services "struggle".
The director of the Welsh Institute for Health and Social Care at the University of South Wales believes the problem will only get worse and said "tricky decisions" could be back in the public domain in 2017.
He said: "Fundamental issues raised, five, 10, even 15 years ago still haven't been resolved.
"We're still running something like 10 intensive care units across south Wales. Now that may be justified but it's quite difficult and expensive to sustain.
"That was flagged up as a problem several years ago and very little has changed, that issue hasn't gone away and has probably got worse."
Health officials have faced protests in recent years over decisions involving hospitals, including:
On wider issues facing the NHS, Prof Longley said the recruitment crisis had got worse, with particular issues for GPs and within specialist services.
He said there needed to be imaginative solutions to rising demand which were not just "reaching for the scalpel or the prescription pad".
Fundamental questions about the way NHS services in Wales are delivered remain unanswered despite being talked about for 15 years, a leading academic says.