Daniel Domscheit-Berg said the organization is plagued by technical and organizational troubles and that core members of the project are talking of leaving, CBS News reported.
Domscheit-Berg had previously been known by the pseudonym Daniel Schmitt and served as WikiLeaks' Germany spokesman.
Germany is important for WikiLeaks, as it receives many of its submissions in German, gets technical support from German hacker group Chaos Computer Club, and a large part of its financial support comes from within the country, CBS News said.
Domscheit-Berg says WikiLeaks founder Julian Assange suspended him a month ago after disagreements about how the site was managed and he has now decided to quit.
"Because of the high pressure we have all been under following the publication of the American military documents, we have not been able to restructure our organization accordingly. This has created a situation in which not all of the work is being done correctly," Domscheit-Berg told a German news magazine.
He hinted he might start a competitor site.
"I will continue to do my part to ensure that the idea of a decentralized whistle-blower platform stays afloat. I will work on that now," he said.
"And that, incidentally, is in line with one of our original shared convictions -- in the end, there needs to be a thousand WikiLeaks."