Geelong and Adelaide have been forced into late changes ahead of the weekend, with injuries hampering both camps on the eve of Round 20.

On Friday Geelong coach Chris Scott confirmed veteran midfielder Sam Menegola won't be available as a potential medical substitute, with a knee injury forcing the Cats into a change to their emergencies.

"On Wednesday he was very, very unlikely, all but ruled out but made a good recovery", Scott told media.

"He's just got a little bit of a sore knee and he made a recovery yesterday to the point where we thought he was some chance, so when that happens we put them in the squad.

"We still thought it was unlikely. If it was likely we would have put him in the team, that's our general practice, and then taken him out once we knew that he wasn't right. But he just didn't quite come up today, so he's not playing this weekend."

Cat Quinton Narkle has been brought into Geelong's 26-man squad to face the Bulldogs, joining Shannon Neale, Luke Dahlhaus and Brandan Parfitt.

GEELONG, AUSTRALIA - JANUARY 13: Quinton Narkle of the Cats in action during the Geelong Cats training session at Deakin University, Waurn Ponds on January 13, 2017 in Geelong Australia. (Photo by Adam Trafford/AFL Media/Getty Images)

Geelong will confirm their final side at 6:25pm (AEST) on Saturday, one hour prior to the bounce at GMHBA Stadium.

Meanwhile, Adelaide have lost young tall Riley Thilthorpe for Saturday night's clash with Carlton at Adelaide Oval.

After injuring his ankle earlier this week the Crows have decided to rule the 20-year-old out of the match, with forward Ellliott Himmelberg brought into the side.

Billy Frampton will come into Matthew Nicks' squad, joining Brayden Cook, Lachlan Sholl and Ben Davis as emergencies for the match.

The Crows host the Blues at Adelaide Oval on Saturday night, with the match to commence at 7:30pm (AEST).