The Sydney Swans have opted for a smaller line-up in defence to oppose Richmond's fleet-footed forward line after selecting Gary Rohan in place of key defender Lewis Melican ahead of Saturday's clash at the MCG.

The Tigers' smaller forward structure has prompted coach John Longmire and the Match Committee to make a more tactical change, omitting Melican despite the young defender's impressive form since debuting earlier this season.

Rohan's addition adds some extra speed to the playing group while allows versatile defender Harry Marsh (the last-minute inclusion for Rohan last week) top retain his spot in the back pocket.

Rohan, who kicked four goals in the Swans and Tigers' last encounter, was a late withdrawal due to illness last week against the Western Bulldogs, but the dynamic forward recovered swiftly to play in the NEAFL Swans' big win against GWS two days later.

He collected 18 disposals and kicked two goals in a positive performance which warranted his selection.

Longmire said while the decision was a difficult one, getting the match-ups right could mean all the difference in Saturday's crunch game.

"We look at the opposition this week, particularly Richmond, they're quite different in their forward setup," Longmire said in this week's Centrum Team Selection.

"They've got a lot of smalls and we wanted to make sure we had a suitable variance in our team to cover those smalls.

"(Lewis) is a bit unlucky but I'm sure he'll be back in the team pretty shortly.

"Gary had a good hit out so it's good to have him back in the team."

Jordan Dawson, Ollie Florent and recently upgraded rookie Shaun Edwards have been named as emergencies.

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