Ashton Agar has been added to Australia's squad for the fourth Test in Sydney as the selectors contemplate a twin spin attack with Nathan Lyon. Agar has not played for Australia since the first two Tests of last year's Ashes series in England, when he made a spectacular debut making 98 batting at No.11, but struggled to have any significant impact with the ball.

The move is surprising given Agar's first-class form - he has taken only seven wickets at 45.14 this summer in the Sheffield Shield and has 62 in his career at 44.00. However, he has impressed during the first few BBL games for the Perth Scorchers this season and Ricky Ponting said this week he considered Agar a bolter for the World Cup squad.

Steve O'Keefe, who made his Test debut against Pakistan in Dubai in October, was unavailable due to a calf injury. O'Keefe has taken nine Sheffield Shield wickets at 28.44 this season, including a five-wicket haul in Adelaide in his first match back from the UAE.

If Agar was to play at the SCG, it would need to be in tandem with Lyon, who bowled Australia to victory in the first Test at Adelaide Oval this month. Captain Steven Smith said Agar had improved his bowling since the Ashes last year, when he played as the sole spinner and Lyon was axed.

"I think he's bowling very well at the moment," Smith said. "He's a good addition to the squad. We'll see how the wicket is in Sydney when we get there and we'll go from there.

"We'll just have to wait and see what the wicket is like. We're not too sure what it will be like. Last year it had a bit of grass on it and previously it's been quite a spin friendly wicket. So I think it's more of a see how the wicket is and if he's needed then he can play."

The addition of Agar is the only change to Australia's squad from the side that secured the Border-Gavaskar Trophy with a draw in Melbourne.