Geelong defender Lachie Henderson and Sydney youngster Isaac Heeney have both experienced pre-season knee setbacks.
The Cats said on Wednesday that Henderson would return to football early in 2018 following a "minor arthroscopy" on his right knee.
It follows mild knee pain in recent weeks following surgery in October.
"While this is a setback for Lachie, it will allow him to move forward on a rehabilitation plan," Cats football manager Simon Lloyd said.
"Lachie will work closely with our medical team over Christmas with the aim to return to football early in the new year."
The Swans similarly announced on Wednesday that Heeney had undergone a "precautionary arthroscope" after the 21-year-old had experienced discomfort during training sessions.
Heeney had minor cartilage damage in a small area, which has been repaired by surgeons.
The Swans said Heeney was expected to rejoin full training in late January.
Meanwhile, Kurt Tippett, recovering from an ankle reconstruction, is "on track" to return to training in February and Lance Franklin, who had surgery on his knee and ankle, will join the main training group after Christmas.
