The vessel was blocked in Crete on Thursday by the Greek coast guard when it stopped to refuel.
"People are fluctuating between moments of great hope and very low morale, particularly when we were stopped," Quentin Girard, a reporter for French daily Liberation, told The Local by telephone.
"If we don't depart again there will be protests, either at the Greek embassy in Paris or the French embassy in Athens."
Girard was on board the Dignite/Al Karama when it was taken to Sitia in Crete by the Greek coast guard, which cited administrative reasons for preventing the vessel from sailing on towards Gaza.
The boat, which is carrying 12 pro-Palestinian activists, had sneaked out of a Greek port early on Tuesday in defiance of a ban on any ships setting sail from Greece in an attempt to run the Israeli blockade.
Girard, whose fellow crew members include far-left politician Olivier Besancenot, said there was "no tension whatsoever" between the activists and the authorities in Sitia.
"The fact that there are several well-known individuals on board means everything is going well," he said. "The main problem is the wait, which is long."
All the other boats which had been expected to participate in a 10-vessel international aid flotilla to Gaza are currently being blocked from leaving ports in Greece, while an Irish boat, which organisers say was sabotaged, is undergoing repairs in Turkey.
The flotilla had been due to set sail last week but was hit by a wave of administrative obstacles which organisers have blamed on political pressure coming from Israel.
Officials in Athens say they imposed the ban for the "safety" of the activists on board in the wake of last year's bloody showdown when Israeli commandos raided a six-ship flotilla in a confrontation that left nine Turkish activists dead.
More than 300 activists from 22 countries had signed up to participate in this year's flotilla, among them dozens of middle-aged and elderly Americans and Europeans.
Israel has made no secret of its determination to prevent the Freedom Flotilla II from reaching Gaza, which has been under a blockade since 2006 after militants there snatched an Israeli soldier who is still being held at a secret location.