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Sydney young gun Isaac Heeney has been forced to go under the knife to address a knee complaint.
The 21-year-old damaged his cartilage during training, which forced him to undergo surgery.
The midfielder had been taking part in full training sessions but underwent an arthroscope as a precaution after experiencing discomfort, according to Sydney's website.
The club expects him to return to full training in late January.
Heeney joins Kurt Tippett and Lance Franklin on the injury list for the Swans, with Tippett expected to return to training by the JLT Cup after an ankle reconstruction and Franklin returning in January from minor ankle and knee surgery.
It's another off-season setback for Heeney, after he missed the start of the 2017 season with glandular fever.
Heeney has played 58 games for the Swans since making his debut in 2015, averaging 17 disposals a match and kicking 60 goals.