The former captain told his fans on social media on Wednesday "see you next year", reporting that his European season is over after he suffered the injury for La Rochelle in a French Top 14 clash against Bayonne at the weekend.
It's the latest in a difficult run of injuries for the 33-year-old stalwart, who had to limp off in the first half in only his second outing since a calf injury had ruled him out for two months from early January.
View this post on Instagram A post shared by William Skelton (@willskel10)
"Season cut short. Thanks for all your messages," Skelton wrote on Instagram. "Always grateful, see you next year."
He followed up the message by declaring: "I'll be back soon, I promise."
"There's a suspected Achilles tendon rupture," La Rochelle assistant coach, Remi Tales, had reported at the weekend.
"It's tough for a player like him, given the effort he's put in to come back after his calf injury.
"We're all thinking of him and hope he recovers quickly, because we need him."
Skelton's message bodes ill for the Wallabies, who had him earmarked as a key pillar amid a busy schedule in 2026.
They kick off their season in July with three Nations Championship Tests against Ireland, France and Italy.
They then tackle Japan in a home-and-away series, travel to Argentina for two Tests and host South Africa for a stand-alone match, before the Bledisloe Cup against the All Blacks.
Skelton, Australia's skipper at the 2023 Rugby World Cup, has had no luck, having also been ruled out of two Tests against Ireland and France in the Wallabies' spring tour last November with an ankle knock.
