Former Sydney co-captain Jarrad McVeigh could miss their AFL season opener for a third straight year, while the Swans could start the season without six of their 2016 grand final side.
McVeigh suffered a calf injury at training, with the club listing the recovery period as three to four weeks and round two as his likely return time.
Sydney start their season in just over three weeks at home to Port Adelaide.
McVeigh also missed the opening round of the 2015 competition with a calf problem and last season a knee issue delayed his first senior start until round four.
He also missed one 2016 finals match with a calf issue, but has logged over 20 appearances in each of the last seven seasons.
Sydney's most senior player with 287 games under his belt, McVeigh stepped down from the co-captaincy this year after six seasons in the role.
Turning 32, next month, McVeigh is the oldest player on the Swans list and it could well be his last year, as his contract expires at the end of this season.
Two other members of the 2016 losing grand final team seem certain to miss round one.
Small forward Tom Papley isn't expected back until round two because of knee and shin issues, while utility Gary Rohan's back and hamstring problems are likely to sideline him until round four.
Three more players from the side vanquished by the Western Bulldogs in the grand final are are no longer on the Swans' list.
Ben McGlynn retired, fellow forward Xavier Richards opted not to accept a new contract and midfielder Tom Mitchell joined Hawthorn.
Young star Isaac Heeney will miss Friday's pre-season clash with GWS Giants because of illness, but star forward Lance Franklin and defenders Dane Rampe and Heath Grundy are among those Swans set to have their first hitout of the year.