The Irish-born backman will have surgery on his lower right leg after being stretchered off the field at Adelaide's West Lakes headquarters on Friday.
"As far as I'm aware to this point, it's around three or four months (out)," Crows coach Matthew Nicks told Adelaide radio station 5AA.
Keane backed into a marking contest and collided with recruit Finbar Maley.
The 25-year-old immediately clutched at his lower right leg before removing his sock and boot and being helped by medicos on to a motorised stretcher.
Keane last season made the AFL's All Australian squad but missed selection in the ceremonial team.
The injury is another blow to the Crows, who have already lost young gun Daniel Curtin for a lengthy period.
Curtin dislocated a knee during a wrestling drill in late January.
The 20-year-old has undergone surgery and will be sidelined until at least round seven of the premiership season.
Adelaide, who were last year's minor premiers but fell from the finals with consecutive defeats, open their premiership season on March 14 against Collingwood at the MCG.
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