The Greens' sluggish preselection process for the inner-northern federal seat of Cooper (formerly Batman) has left the party without a candidate just months out from a federal election.

David Risstrom, a Melbourne barrister and former Greens councillor at Melbourne City Council, was preselected late last year to replace six-time candidate Alex Bhathal as the Greens' pick for Cooper.

But despite a federal election looming, the party has yet to formally announce Mr Risstrom's candidacy for a seat that, less than a year ago, it was on the cusp of wresting from Labor.

It's understood the party is undergoing painstaking probity work on Mr Risstrom, including vetting and clearances.