Teacher shortages need to be addressed before schools face major problems, the teaching regulator has said.
Figures show recruitment to secondary school teacher training courses was more than a third below the target for the second year in a row.
The chief executive of the Education Workforce Councils said a national campaign to attract more people to the profession is needed.
The Welsh Government said the teacher vacancy rate is “comparatively low”.
Wales’ three teacher training centres recruited 538 students to secondary school teacher training courses, starting in September 2016, Higher Education Funding Council for Wales figures show.
This represents a 38% shortfall on the target of filling 871 places, following a 37% shortfall in 2015-16.
Universities reported filling 683 primary teacher places despite a target of 750, a similar picture to last year.
Hayden Llewellyn, chief executive of the Education Workforce Council, said the situation was not yet a “crisis” but issues needed to be addressed.
The council is the regulator for the teaching profession and keeps a register of those working in education in Wales.
Mr Llewellyn said the key areas of concern are around recruitment of newly qualified teachers, head teachers, science and modern languages teachers and Welsh medium teachers.
“It needs to be monitored,” he said.
“We are seeing some of these issues that previously we didn’t have.
“In the past we always had an oversupply of people wanting to be teachers. It’s acknowledging that this situation was different to 10 years ago.
“We haven’t got a crisis, we’ve got some issues. The key is to start to address them before we get a major problem.”
Plaid Cymru leader Leanne Wood last month said there was now a “crisis” in teacher training in Wales.
Teaching unions have claimed the stress and workload associated with teaching has deterred people from joining the profession.
Another key issue according to Mr Llewellyn is a scarcity of permanent jobs for newly qualified teachers.
He said: “An obvious area to look at would be that rather than new teachers starting on a supply basis or a temporary contract basis, to give them permanent employment.
“That would be a clear signal that teaching is a rewarding career and you start with a permanent job”.
A Welsh Government spokesman said the overall teacher vacancy rate in Wales remains “comparatively low” despite some “local difficulties” in recruiting in certain subjects or sectors.
“We want teaching in Wales to be a first choice profession so we attract the very best,” it read.
“We are working closely with partners including regional consortia and local authorities to identify and address issues relating to recruitment and retention.”
Financial incentives are offered to graduates with the highest level of subject knowledge.