ESSENDON star Zach Merrett has been ruled out of the rest of Friday night's clash against Adelaide at Etihad Stadium due to concussion.

The Bombers midfielder felt the full affects of a bump from Crow Richard Douglas in the first quarter of the game, leaving him dazed and needing to be helped off by medical staff.

Douglas was reported for rough conduct in the collision.

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Merrett was unable to brace himself for contact as Douglas cannoned into him, although it is arguable whether the contact was to the Bomber's head or the neck/shoulder region.

It will be a challenging case for Match Review Officer Michael Christian to determine, because of the doubt about where the contact was felt.

Merrett suffered a case of blurred vision when he copped a head knock against Richmond in the Bombers' first JLT Community Series game on February 23, while he was forced from the track briefly after a knock to the head at training in January.

The midfielder was placed in the concussion protocol following the game against the Tigers, but returned for the second pre-season match against Geelong in Colac on March 11.

WATCH: Merrett's head knock during the pre-season

Merrett was keen to return to the field to play out the match against the Crows, but after doing some ball work in the rooms and being assessed, club doctor Bruce Reid determined he was not right to come back onto the ground.