GEELONG has decided to take a cautious approach with Tom Lonergan, withdrawing the key defender ahead of its duel against Collingwood at the MCG on Saturday.

The key backman was replaced by small defender Tom Ruggles in Geelong's selected side.

Lonergan was concussed in the opening minutes of last Friday's showdown with Adelaide at Adelaide Oval after clashing heads with teammate Lachie Henderson.

The backman trained fully at the club's new training facility at Deakin University on Thursday and it is understood he had passed his concussion test.

But with Lonergan suffering three concussions in the last three years, and with the latest research surrounding head knocks, the Cats opted for a no-risk policy.

The Cats and Magpies will renew hostilities at 1.45pm.