Australia's star signing Iain Jensen could miss the SailGP season's first three regattas with a knee injury suffered ahead of the Perth event.
The Olympic gold medallist has been told to prepare for up to eight weeks out of the water after he slipped and hurt his left knee during Thursday's practice on Fremantle Harbour.
Only hours before racing was due to begin on Saturday, Jensen was officially ruled out of the Perth SailGP that begins the high-speed sailing's sixth season.
He watched from the shore as Australia finished Saturday in fourth place on the event leaderboard, hoping to be one of three boats to advance to Sunday's event final.
Jensen had left Great Britain this campaign for a first chance to sail under the Australian flag, after an earlier Olympic career that yielded a gold medal win in 2012.
The 37-year-old was in good spirits despite the 11th-hour blow that has delayed his fairytale homecoming.
"I was joking with Tom (Slingsby, skipper) before, I said 'I've never missed a race through injury or illness and I've sailed two days with you and I'm out for eight weeks'," Jensen told AAP.
"Considering it's only a couple of days after, (the injury) feels pretty good. I've had a lot of good support from the SailGP doctors and physios."
Jensen is still hopeful of speeding up his recovery to take the water at the season's second event, to be held in Auckland on February 14 and 15.
But if he requires the full eight weeks out, Jensen will miss that event as well as the Sydney SailGP to be held between February 28 and March 1.
"I'm still holding out hope for Auckland in four (weeks) with a good brace," he said.
"Initial thoughts are recovery is probably around eight weeks but there's maybe potential to speed it up with good physio and good rehab, and the use of a brace."
Jensen has joined Australia's team staff on shore in Fremantle to assist with communications across the two days of the Perth SailGP.
His absence looms as a big blow for an Australian team fighting to bounce back from consecutive losses in the league's winner-take-all grand final race.
Jensen's Great Britain boat defeated the Australians and New Zealand to claim a $2.99 million jackpot in that race in Abu Dhabi in November.
Jensen was replaced by 48-year-old veteran Glenn Ashby for this weekend's races after the Olympic silver medallist flew out to join the team early on Friday morning.
Slingsby was pleased with Ashby's performance as Australia won the first fleet race and placed second in the last on Saturday.
"(Jensen) has really injured his knee and he's going to have to rest up for a while," Slingsby said.
"But we're so lucky we can ring someone like Glenn Ashby and he can fly in on such short notice and we're in the game and being competitive."
AAP's reporter travelled to Perth as a guest of SailGP.
