Sydney coach Paul Roos says getting consistency from his younger AFL players is his biggest challenge as he prepares to blood Kristin Thornton against Carlton at the SCG on Saturday.

The inclusion of 21-year-old utility Thornton in place of the injured Jared Crouch (hamstring) is the only change to the side beaten by Brisbane last weekend.

Key forward Barry Hall didn't train on Thursday because of a niggling groin problem, but Roos expects his spearhead to play on Saturday.

The Swans have lost two of their first three games, while the emerging Blues have a 2-1 win-loss record.

Impressive Sydney midfielder Brett Meredith made his debut in round two, while fellow youngsters Craig Bird, Kieren Jack and Ed Barlow are in the early stages of their careers.

Sydney's attempts to inject even more youth into their group has been hampered by injuries to several of their up-and-coming players.

"My biggest challenge now as a coach is to try and eradicate that inconsistency with that younger group," Roos said.

"I think the senior players have all been pretty good.

"Obviously we'd like some to play a little better but certainly that level of youth brings a level of inconsistency, we're already seeing that early in the season.

"We've got a younger team coming now and my job and our coach's job is to get those seven or eight younger players playing finals footy as quickly as we possibly can."

Thornton has fought his way back from a knee reconstruction last year and was recently promoted from the rookie to the senior list.

Roos said Thornton was a versatile player who could operate on the wing, at halfback and could play tall.

"He's quite a versatile player, he's also a really composed player, a good decision-maker," he said.

Roos also admitted there was an element of frustration in the weekly battle to get Hall fit after the veteran forward had such an encouraging pre-season.

Hall tweaked his groin in the round two win over Hawthorn.

"Hopefully he will play this week and I'm pretty sure he will, but at some point you do have to make the decision," Roos said.

"The difference is this time it's not an osteitis-type injury, it's more just a muscle-type injury, but you definitely have to make a decision at some point if it keeps rumbling on.

"You don't want to have 15 average weeks when you could miss one or two and have hopefully 13 really good weeks.

"Hopefully we're not at that stage at the moment, but it is a bit frustrating for him and frustrating for the club."

Midfielder Luke Ablett, who was a late withdrawal from last week's game with a buttock injury, was listed as an emergency along with former Canadian Test rugby back Mike Pyke.

After having their lengthy winning streak against Brisbane snapped last week, Roos dismissed Sydney's recent historical dominance over Carlton, who have lost their last 11 to the Swans, including their last six at the SCG.

He expects the emerging Blues to become a very good side over the next five-to-six years.

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