Three changes have been confirmed for Collingwood’s trip to South Australia to take on Port Adelaide.

All stem from last weekend’s win over North Melbourne. Daniel Wells (quad) and Levi Greenwood (knee) will miss with injury, while ruckman Brodie Grundy sits out the first of a two-game suspension.

Their replacements are a trio of players who have strung together strong VFL form in recent weeks.

First-year Pie Callum Brown has averaged 23.3 disposals per game after experiencing his first taste of AFL football in June.

Remarkably, in just his third game, Brown will meet a side he's already played against. The 19-year-old had nine disposals and kicked his first senior goal against the Power in round 14.

Mason Cox has used his time in the VFL to hone his ruck skills in recent weeks, while James Aish will be rewarded with his sixth senior game this season after impressive performances for the VFL Magpies.

Collingwood coach Nathan Buckley believes Cox will relish the challenge of taking on in-form Port Adelaide ruck Paddy Ryder.

“It’s a great opportunity for him to show his ruck development over the last couple of years,” Buckley told the media on Thursday.

“He and Darcy (Moore) will share that responsibility.

“It’s a fantastic opportunity for him and a chance to take the next step in his AFL journey.”

Port Adelaide v Collingwood
Round 21 2017
Sunday 13 August
Adelaide Oval, 4.40pm (ES)

IN: James Aish, Callum Brown, Mason Cox
OUT: Brodie Grundy (suspended), Levi Greenwood (knee), Daniel Wells (quad)

Collingwood
B: Jeremy Howe, Lynden Dunn, Tom Langdon
HB: Jack Crisp, Tyson Goldsack, Brayden Maynard
C: Steele Sidebottom, Taylor Adams, Will Hoskin-Elliott
HF: Josh Thomas, Ben Reid, Jordan De Goey
F: Jamie Elliott, Darcy Moore, Alex Fasolo
Foll: Mason Cox, Callum Brown, Adam Treloar
Int: Jarryd Blair, Matthew Scharenberg, James Aish, Tom Phillips
Emg: Josh Daicos, Tim Broomhead, Josh Smith

Ruck and roll
Collingwood’s ruck division will be carried by Mason Cox, who last appeared at senior level against Essendon in round 16.

He is averaging 22.7 hitouts in nine VFL games this year, and has enjoyed a purple patch in recent weeks, averaging 34 hitouts and 20 disposals in his past three games.

Cox has also kicked a goal in all bar one of his nine VFL games, with a high of six against Port Melbourne in round 10.

Get Wells soon
Collingwood will be without two of its most experienced midfielders this weekend.

Levi Greenwood will sit out the next 2-3 weeks due to his knee complaint, while Daniel Wells’ quad injury will sideline him this weekend.

Brodie Grundy, meanwhile, will not appear until the final round of the year after accepting his two-week suspension.