In an interview with private broadcaster B92, Nikolic quoted EU envoy Miroslav Lajcak as saying that adhesion talks with Serbia would probably not start in the autumn or by the end of the year as wished by Belgrade.
Serbia applied for EU membership in 2009 and was granted candidate status by EU leaders earlier this year.
EU conditions, the president also told the television network, concern the abolition of Serbian parallel institutions in northern Kosovo and the effective implementation of all agreements between Belgrade and Pristina.
EU-sponsored talks between Serbia and Kosovo started in March 2011 but were suspended before the May 6 national elections in Serbia and should resume once the new government is formed.
Montenegro began EU membership talks on June 29. Island and Turkey are also candidates. (ANSAmed)