Running defender Nick Smith will replace the injured Ben McGlynn for Saturday's clash against West Coast.

Smith impressed when given his chance in the second half of 2009 and Roos said the youngster's elevation was just reward for his outstanding form in the reserves, which included a 37-disposal effort last weekend.

"I think he knew he wasn't going as well as he would have liked through that early part of the pre-season Cup and he did a lot of work," he said.

"We asked Nick to do a few things, go back, and he's been really good the last month. He just forced his way in, really, with his performance and with Benny going out.

"That running power that [McGlynn] has got means we probably haven't got that same player in the seconds, so we'll have to just adjust our senior team a little bit and Nick can come in as the form player in the seconds."

Roos said he was expecting a spectacular contest against the Eagles, and hoping for a large Saturday afternoon crowd at the SCG.

Roos is backing his ruckman, Mark Seaby and Shane Mumford, to take on West Coast pair, Dean Cox and Nic Naitanui.

He says there is little point planning to combat Naitanui because he simply doesn't know what the high-flying Eagle will do.

Roos said on Thursday that he would spend more time preparing his own players than worrying about how to nullify Naitanui.

"I'm sure John's [Worsfold] not sure what Nic can do and what he can't do ... so there's no point in me putting an enormous amount of time into him because I really don't know what he's going to do, " Roos said before training on Thursday morning.

"I've got to spend more time on my players that I have a bit more information about."

The Swans' dual Brownlow Medallist Adam Goodes looms as an ideal counter for Naitanui if the young Eagle continues his hot form on Saturday, but Roos was lukewarm on the idea of sending his star back into the ruck.

"[Goodes] did some extraordinary things as a ruckman and everyone's saying some of those things that Nic's done we've never seen before, but if you go back over Adam's tapes, they're pretty good," he said.

"Nic's a big guy and I really think we should leave that to 'Seabs' and 'Mummy' because they're both big guys.

"Adam has been terrific as a midfielder and terrific as a forward so I think that's the role we'll continue to play at this stage."