Although the Australian Rugby Union (ARU) has yet to be notified of a change in ownership, the governing body says it has received confirmation of a sale via a third party.
In a statement issued on Friday night, the ARU said it understood the ownership has been transferred from Cox's Imperium Group to the Victorian Rugby Union.
"The Melbourne Rebels have an obligation under their Participation Deed to inform ARU of any change of ownership," the statement said.
"To date, ARU has received no such communication from the Melbourne Rebels despite recent attempts to confirm their position.
"ARU is urgently seeking to confirm the terms on which this transfer occurred."
The Rebels' future in Super Rugby is under threat after a decision to cull an Australian team.
The Rebels or Perth-based Western Force will be cut, in accordance with a promise made to SANZAAR to streamline the 2018 competition.