Mills will not see any AFL action until after the Swans' bye in round three after scans revealed he tore his plantar fascia, the club confirmed on Tuesday.
The 27-year-old had been battling the foot injury in recent weeks but was optimistic about his chances of lining up against Hawthorn at the SCG on March 7.
He did not play in last week's match simulation against GWS.
"Callum had been managing his plantar fasciitis well, however he required follow up imaging with the results last night revealing Callum has sustained a tear of the plantar fascia," Swans physio Damian Raper said in a club statement.
"After consultation with our medical team, we believe the best course of action is to spend two weeks in a boot, before reassessing Callum's return to play program."
It continues a torrid run with injury for Mills, who played only seven games last season.
He spent eight months on the sidelines after tearing the rotator cuff in his left shoulder in a 2023 'Mad Monday' incident.
After a low-grade calf strain delayed his return, Mills finally made his comeback in round 18 against North Melbourne.
It was a hamstring injury that ended his already short 2024 campaign early, missing the Swans' preliminary final win over Port Adelaide and their grand final defeat.
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