St Kilda has made one change ahead of this Sunday’s must win game against Melbourne at the MCG, with experienced defender Sam Gilbert replacing the injured Nick Riewoldt.

After announcing his decision to retire at the end of this season, Riewoldt sustained a concussion in the last quarter of last Sunday’s thrilling win over West Coast and hasn’t passed the required concussion tests this week.

The Saints expect the six-time Trevor Barker Award winner to be fit to return against North Melbourne next weekend in what could potentially be the second last game of his decorated career.

Gilbert, 30, returns to bolster the Saints’ defence after missing the last three games against West Coast, Port Adelaide and Sydney due to a hand injury.

After being acquired as an unrestricted free agent last October, full back Nathan Brown has slotted in seamlessly to St Kilda’s back six, forming a formidable partnership with fellow fresh face Jake Carlisle.

Brown, who helped lead Collingwood to premiership glory at the Saints expense in 2010, will play his 150th game when he runs out on the MCG on Sunday and with Jesse Hogan absent, he is likely to spend time on Tom McDonald or Sam Weideman.

With so little separating so many, this weekend’s clash looms as an elimination final before the finals. The loser will essentially remove themselves from the race to September, while the winner will remain alive and continue the chase of 8th placed Essendon.

Friday Microscope: Round 21 v Melbourne

Round 21 Squad v Melbourne
Sunday August 13 at 1.10 pm
MCG

B: Jarryn Geary, Nathan Brown, Dylan Roberton
HB: Jack Newnes, Jake Carlisle, Jimmy Webster
C: Shane Savage, Luke Dunstan, Jack Billings
HF: Jack Steele, Josh Bruce, Maverick Weller
F: Jade Gresham, Tim Membrey, Jack Sinclair
R: Billy Longer, Seb Ross, Jack Steven
Interchange: Blake Acres, Sam Gilbert, Koby Stevens, Brandon White
Emergencies: Tom Hickey, Daniel McKenzie, Jack Lonie

IN: S. Gilbert
OUT: N. Riewoldt (concussion)

Milestone: N. Brown – 150 games