Sydney will unleash its three-headed ruck monster for just the sixth time in five seasons on Sunday when the injury prone Stephen Doyle is set to make his AFL return against Geelong at the SCG.

The 204cm giant has played only 20 games in four seasons, mainly due to a succession of knee problems.

Coach Paul Roos was savouring the rare prospect of fielding his full strength ruck trio of Doyle, Jason Ball and Brownlow medallist Adam Goodes against early season straggler Geelong which is missing its key big man, Steven King.

Roos said he would be able to move Goodes around the field and utilise the varied talents of his three big men, who haven't played together since round one last year when Doyle injured his knee.

Roos suggested Goodes and Ball would handle most of the ruck duties against the Cats, with Doyle helping out in that department but playing primarily on the forward line.

South Australian Doyle, 22, said he had never lost confidence in his body despite not having ever played more than five successive senior games or nine in a full season.

"I've always had confidence in my body, some of the injuries I've had have been out of my control and just sort of happened on the day and I couldn't really do much about it," Doyle said.

"But I'm feeling pretty confident that I will be able to string a few games together. My body is feeling good now and I've lost a couple of kilos and fitness wise I feel pretty good."

Youngster Lewis Roberts-Thomson was expected to make way for Doyle, who admitted he belonged to the old fashioned "big log" style of ruckman.

Roos was also adopting a cautious approach with star forward Michael O'Loughlin who suffered a hamstring injury against Fremantle last week.

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