He said he expected headway in how the crisis was being dealt with, but not a definitive answer.
"Europe is evidently going for a higher level of political and financial integration," Milanovic told reporters upon arriving in Brussels.
He did not rule out the possibility of a new constitutional framework when Croatia joins the EU in a year's time. "At this moment, we can't say what will be in a year's time when we join. It's possible that there will be another European constitutional framework."
Milanovic said that a monetary union could work without stronger fiscal ties in good times, but not in times of crisis.
The EU leaders will also formally approve the opening of accession negotiations with Montenegro, which will be opened on Friday.