WHEN Chris Scott heard Sam De Koning was in line for a milestone match this weekend the reason for celebration wasn't what the coach expected.

Now 23 years old and with a premiership behind him, De Koning seems to have been a part of the Cats' lineup for a long time, however, Saturday's clash against Carlton – and brother Tom – will only be De Koning’s 50th outing at AFL level.

It will be the third time the siblings have faced off, with the win tally currently sitting at one apiece.

"I really think of Sam being a mainstay of our team and it sort of took me by surprise," Scott said on Friday.

"When someone said he had a milestone, I was hedging more towards (it being) 100 than 50.

"He's a very young player, there's a lot of footy in front of him, but he's already crucial to us.

"There's no better stage (for the milestone). I don't know how he feels about playing against his brother - I don't bring it up with him - but more important is you get to play in front of a virtually sold-out MCG on a Saturday afternoon.

"It's pretty cool."

Geelong's star defender Tom Stewart is unavailable because of concussion protocols while No.1 ruckman Rhys Stanley and Zach Tuohy will return to action against the Blues.

Premiership midfielder Cam Guthrie is also back for his first game in 12 months after recovering from last year's foot surgery and a pre-season quadriceps injury.

"He's been in full training for well over a month with a plan to get him straight back into the AFL team," Scott said.

"It's been a well thought through process and this has been the plan all along.

"You could say he hasn't played AFL football for a long time, but that would be ignoring the pre-season and the preparation he's had over the last six weeks in particular."