COLLINGWOOD has suffered another injury, with Nathan Brown believed to have damaged his medial ligament to his already reconstructed left knee during the match against the Brisbane Lions at the Gabba.

Brown fell awkwardly during the second quarter when he was pushed out of a marking contest, landing under teammate Harry O'Brien.

The key defender's left leg twisted and he was assisted from the field limping heavily.

The Magpies activated sub Peter Yagmoor for Brown, who was playing just his third match in 2012.

Magpies coach Nathan Buckley admitted he was concerned when Brown went down but he said there were some small reasons for optimism.

"When Browny goes down you fear the worse because he's had some wretched luck," Buckley said.

"Our medicos believe he's going to come out of it better than he might have otherwise, so we'll have to wait for the dust to settle and see how exactly that falls."

Brown will join fellow backmen Ben Johnson and Chris Tarrant on the sidelines, although Ben Reid made a successful return from injury against the Lions.

Heath Shaw said the depth the Magpies had developed would ensure the team could cover the loss of some of its prime movers in the back half.

"Obviously, Browny's going to be a loss but we've showed in the past that Lachlan Keeffe can play down there, Reidy came back and Maxy (captain Nick Maxwell) can still play on the big guys as well," Shaw said.

"We're confident our back six or seven can take on any forward six on any given day."

Shaw also believed his team's ability to rebound from defence was still in tact.

"The run ... through Harry [O'Brien] and Marty Clarke coming back into the system and even Yags (Yagmoor) in that last half showed a bit as well," Shaw said.

"The good thing about our back line is we don't just rely on one person coming out of the backline, we rely on every one."

The views in this article are those of the author and not necessarily those of the AFL or its clubs