KIEREN Jack is a huge late withdrawal for the Sydney Swans, missing Saturday's season-opening match against Greater Western Sydney with a sore back.

The Swans' co-captain, who hasn’t missed a game in more than two seasons, woke up on Saturday morning with a sore back and won't line up in the fifth instalment of the Sydney derby.

It comes after the news that Alex Johnson again hurt his knee earlier in the reserves' match against GWS, his first game since the 2012 Grand Final following two knee operations.

The severity of Johnson's injury is not yet known on a day when both teams will aim for a strong start to the year and the Swans will unveil Lance Franklin for the first time.

The Swans at least have a more than handy replacement for Jack, with former All Australian and Norm Smith medallist Ryan O'Keefe – a surprise omission from the original side selected – coming in as a replacement.

O'Keefe will start as the Swans' substitute, with Tom Mitchell, Harry Cunningham and Dane Rampe on the bench for the opening bounce at Spotless Stadium.

For the Giants, gun midfielder Dylan Shiel is a surprising substitute in coach Leon Cameron's first official match at the helm, with Tom Bugg, Stephen Coniglio and GWS debutant Josh Hunt starting on the bench.

GWS is hoping for a crowd in excess of 20,000 for the match, which would destroy the previous record at the ground of 12,314 for the round 22 match against Richmond last year.