Turkey's prime minister has been given a coded warning not to stand for president by an influential panel of senior Turks, correspondents say.
The Turkish PM is a practising Muslim in a secular republic
The higher education board, which includes the rectors of all Turkey's universities, said the president must uphold Turkey's secular values.
But PM Recep Tayyip Erdogan hails from an Islamist party, and some fear he may pursue a pro-Islamic agenda if elected.
Candidate registration begins later this month, with the vote due in May.
The board did not name Mr Erdogan in its statement, instead saying only that the president must be someone who upholds the fundamental principles of the Turkish Republic, above all the principal of secularism.
But the BBC's Sarah Rainsford, in Istanbul, says Mr Erdogan is the most likely candidate to win the presidential election and this was clearly a warning shot fired against him by a key force within the Turkish establishment.
The secular elite of Turkey has declared him a threat to the regime, claiming the religious-minded prime minister harbours a pro-Islamic agenda that could transform the country.
The rectors' statement came as prosecutors announced they will not pursue criminal charges against the prime minister over a comment made in an interview seven years ago.
Mr Erdogan's party said the opposition were attempting to undermine any attempt to win the presidency.