Rioli Jnr has returned to the Tiwi Islands to be with his family and is unavailable for the Eagles' clash with Hawthorn at the MCG on Sunday.
In a statement on Wednesday, the Eagles said they were "devastated" about Rioli Snr's passing.
"The Rioli family has been an intrinsic part of our club since Willie Jnr joined us in 2017 and the coaches, players, staff and board are deeply saddened by the sudden death of Willie Snr," West Coast said in the statement.
"Willie Jnr will take indefinite leave to join his family in the Northern Territory and our club will do everything possible to support him.
"We extend our love and condolences to Willie, his mother Georgina and the extended Rioli family."
A 2018 West Coast premiership player, Rioli Jnr has featured in 10 games this season and kicked 14 goals.
The 27-year-old returned in round one after serving a two-year ban for tampering with urine samples.
Rioli Snr is a Northern Territory football great who was drafted by Hawthorn in 1990 but never played an AFL game.
He also represented South Fremantle in the WAFL.
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