It will have a certain but not a significant effect, Seks told Croatian Radio.
The parliament speaker said that meeting international criteria was the most important thing on Croatia's path to the EU.
The assessment of Croatia's meeting those criteria will depend on how crucial EU countries, notably Great Britain and countries supporting it, will assess the report of the ICTY Chief Prosecutor, Carla del Ponte, Seks said.
"I can assume that the report will be very restrained regarding the critical area where Croatia is trying to prove that it is credible in meeting its obligations towards the International Criminal Tribunal for the former Yugoslavia," Seks said.
He stressed that Croatia had tried and was still trying to prove that it was cooperating with the Hague Tribunal, but that the term cooperation did not mean the acceptance of "entirely inappropriate and untrue revisions of Croatia's history", notably in the so-called explanation of the indictment against Croatian Army Generals Mladen Markac and Ivan Cermak.
Seks said that the Croatian Government must do everything to contest what he called forgeries with all legal means.
He stressed that Croatia would firmly contest the allegation that Operation Storm was a criminal enterprise in which Croatia's entire former political, military and police leadership had taken part.
Seks said that a possible slowing down of Croatia's integration with the EU would not be a negative mark only for the prime minister and the government, but for the entire political scene in Croatia.
He reiterated that all political forces in parliament wanted to see Croatia join the EU.