An England and Wales Cricket Board spokesman confirmed the absence which has seemed inevitable ever since scans last weekend showed Overton had suffered the hairline fracture during the third Test in Perth.
The 23-year-old seamer had already been hit on the chest while batting in Adelaide, but it was when he fell awkwardly trying to take a caught-and-bowled chance at the WACA that he exacerbated the injury.
After England’s series-sealing defeat, Overton revealed he had been told he could suffer a punctured lung if he dived and hurt himself again in the same place.
His unavailability for what would have been his third Test appearance leaves uncapped Tom Curran most likely to replace him - with fellow fast bowler Mark Wood, recovering from a heel injury, and young leg-spinner Mason Crane also in the equation as England try to avoid a 5-0 Ashes whitewash in the last two matches.
A brief ECB statement read: “Official confirmation that Craig Overton (is) ruled out of this Test match with a fractured rib sustained at the WACA.”
Teams for the fourth Ashes Test, starting in Melbourne on Boxing Day at 10.30am (Christmas Day, 11.30pm GMT):
England (probable): JE Root (Captain), AN Cook, MD Stoneman, JM Vince, DJ Malan, JM Bairstow (wkt), MM Ali, CR Woakes, TK Curran, SCJ Broad, JM Anderson
Australia (probable): S Smith (Captain), D Warner, C Bancroft, U Khawaja, S Marsh, M Marsh, T Paine (wkt), P Cummins, N Lyon, J Hazlewood, J Bird
Umpires: K Dharmasena (SL) and S Ravi (Ind). Third umpire: J Wilson (WI). Match referee: R Madugalle (SL)