Victoria's top cop will appear before a royal commission into the police force's use of lawyer Nicola Gobbo to inform on her underworld clients.
Chief Commissioner Graham Ashton is scheduled to give evidence about the 'Lawyer X' scandal on Monday and Tuesday.
Mr Ashton is one-of-three current and former chief commissioners to be grilled by the inquiry, alongside his predecessors Simon Overland and Christine Nixon.
Commissioner Margaret McMurdo is examining how Ms Gobbo informed on her gangland clients on-and-off, officially and unofficially between 1995 and 2012.
The inquiry has ruled the turncoat barrister is not ill enough to get out of giving evidence over the phone in January.
Ms Gobbo's lawyer had argued her client was too physically and mentally unwell to do so but Ms McMurdo was not convinced.
While the commission cannot force Ms Gobbo to appear, it can recommend criminal charges against her for failing to comply with the order.