Naismith underwent surgery on a third ACL injury last year, with the 29-year-old last featuring for the Swans in Round 4, 2020.
The club confirmed on Thursday that the North Shore product will remain sidelined for the entire season, with Naismith still requiring a lengthy period of rehabilitation to return to playing capabilities.
“Sam has shown incredible commitment and resilience in his mission to return to elite football, but his recovery is still going to take some time from here,” Swans football boss Charlie Gardiner said.
“Sam is currently five months into a 12 month rehabilitation program, and given this is Sam’s third knee reconstruction, we will be taking a conservative approach to maximise his chances of making a full and successful recovery.”
Naismith made his AFL debut with the Swans in 2014, playing in the club's final game of the home and away season against Richmond.
The 205cm tall veteran faced setbacks the following year before breaking into John Longmire's side in the back end of 2016, playing a further 12 games.
Naismith had held a key role in the Swans' best 22 in 2017 before being limited to more time on the sidelines, having played just two games since.
The Swans' ruck stocks have been buoyed by the arrival of Peter Ladhams from Port Adelaide this off-season, with Callum Sinclair and first-string tall Tom Hickey set to contend for ruck duties this year.