JUST days after being ruled out for the rest of the season, Geelong's Daniel Menzel has gone under the knife yet again.

The 22-year-old had the surgery in an attempt to be fully fit for pre-season training, and he remains committed to returning to the field in 2015.

"Dan's had a minor procedure this morning on his knee," Cats physio Mike Snelling told CatsTV on Tuesday.

"It was basically just to clean up some scar tissue around his latest surgery around the patella tendon, and we expect him to be back on track within a month or so.

"It's a little setback for him, but hopefully it's nothing major.

"We don't anticipate that it makes too much difference to his ability to return to play."

Geelong is continuing to monitor the fitness of key defender Tom Lonergan, who was concussed during Friday night's win over North Melbourne.

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Lonergan copped two accidental knocks from North's Leigh Adams and had to be subbed out of the game at quarter-time.

The Cats have not ruled him out of Thursday night's clash with the Sydney Swans at the SCG, although he is considered very unlikely to play.

All will be revealed when Chris Scott and his men fly out of Melbourne Airport on Wednesday afternoon.

"I think it's important to say publicly… if Tom (Lonergan) makes the trip, he's absolutely ready to play," Scott said.

"If there's any doubt at all… he won't play."

The Cats won't be able to consider Jordan Schroder for the trip to Sydney.

The emerging midfielder was tipped to play his first AFL game of the season against the Kangaroos last weekend, only to strain his calf in the last training session of the week.

"It was a fairly innocuous sort of injury, really," Snelling said. "Unfortunately, he felt a little ping in his calf, so he's got a calf strain.

"We're treating that and he’ll be a little bit away from running, but he's getting there slowly.

"He'll be a few weeks."

Fellow midfielders Josh Caddy and Allen Christensen are closer to playing again.

Christensen, who had back surgery during the pre-season, is back in full training.

The Cats' VFL team has a bye this weekend, so he is expected to return to action via the VFL the following weekend.

Caddy, who suffered a broken foot at training in mid-April, is not yet back in full training, but he has been completing some running sessions at Simonds Stadium.

"Once he's in squad training, (he'll need) to get a little bit of conditioning back and hopefully then we'll see him return to game-day," Snelling said.

Twitter: @AFL_AdamMcNicol