Lance Franklin has undergone a knee arthroscopy with Sydney admitting the superstar forward is not a certain starter for Round 1 of the AFL season.
Franklin was sent for scans having reporting back to the club with a sore knee and subsequently went under the knife on Monday.
The Swans expect Franklin, who turns 33 later this month, will resume full training in approximately 10 weeks.
"Which means he remains a chance to play in Round 1 but we clearly can't make that call until closer to the date," Swans football manager Charlie Gardiner said.
"We weighed it up and felt that it was best for Lance to have a clean-up now, so he underwent an arthroscope.
"We may have been able to manage the knee through the year, but we're hopeful that this will mean Lance can have an uninterrupted season.
"He has had a similar clean-up on his right knee in the past, so there are no long-term concerns."
Sydney, who missed the finals for the first time since 2009, start their season against Adelaide at Adelaide Oval on March 21.
It is the second year in a row their gun forward's preparation for a season has been put on hold because of surgery.
Franklin had off-season groin surgery prior to the Swans' 2019 campaign, in which he only played 10 games because of hamstring injuries.
The setback comes after Franklin enjoyed one of his healthiest starts to a pre-season since leaving Hawthorn in 2013 to join the Swans on a nine-year deal worth approximately $10 million.
The four-time Coleman medallist returned to training in November, ahead of schedule and alongside the club's youngsters, and declared last month that he was confident of returning to his best in 2020 and beyond.
"There's no doubt in my mind," he told AFL.com.au
"I'm as hungry as ever and I've got no doubt that if my pre-season continues like this that I'll have a strong year.
"Some people might think otherwise but I still feel young and fresh."
Gardiner suggested 32-year-old Franklin's fitness base from the past two months would help him get back on the park soon.
"He had been training extremely well to date, so we expect that will assist in his recovery," he said.