The star onballer has bone bruising and an arthroscopy this week will show the extent of the injury.
It is a massive addition to an already worrying casualty list for the Power, who have lost Todd Marshall for at least half the season with an Achilles injury.
Brandon Zerk-Thatcher (back) and fellow defender Esava Ratugolea (knee) could also miss round one.
Butters, third in the Brownlow Medal count last season, is one of the league's best players.Â
After making a preliminary final last season, Port have confirmed the coaching succession plan where Ken Hinkley will hand over to Josh Carr for next year.
Also on Tuesday, luckless Sydney captain Callum Mills was ruled out of the opening round after suffering another injury.
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 and their grand final loss.
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