Egypt was expecting Ahmed Abul Gheit, the last foreign minister to serve under ousted Egyptian president Hosni Mubarak, to be chosen unanimously by the 21-member pan-Arab body.
But in a surprise setback to his candidacy, Qatar expressed reservations due to Abul Gheit's "hostile positions", an Arab diplomat said on condition of anonymity.
Relations between Doha and Cairo have soured since the army's ouster of Egyptian president Mohamed Morsi in 2013.
Cairo blames Doha for supporting Morsi's outlawed Muslim Brotherhood movement, the target of a brutal police crackdown since the Islamist's ouster.
Several diplomats told AFP that Doha accused Abul Gheit of pushing Egypt to boycott a Qatari-proposed Arab summit in 2009 to discuss an Israeli offensive against the Palestinian Gaza Strip.
Unlike the charismatic ex-chief of the Arab League, Egyptian Amr Moussa, who was known for his tough positions on Israel, Abul Gheit has often faced criticism for adopting a relatively softer approach towards the Jewish state.
In 2008, he even accused Hamas of being responsible for the Israeli war on Gaza.
Egypt proposed Abul Gheit, 73, for the post after fellow Egyptian Nabil al-Arabi declined a second five-year term as secretary general. His present term ends in July.
Arab diplomats told AFP that in the absence of a unanimous choice, Egypt is asking for a vote on Abul Gheit's candidacy. To be appointed, two-thirds of League members have to vote in his favour.
