Australia paceman Pat Cummins has been ruled out of his team's clash against Sri Lanka, while Mitch Marsh is fit and ready for the Cricket World Cup encounter.

Captain Michael Clarke was unable to name his final 11 at the pre-match media conference on Saturday, but he confirmed Cummins would miss the game.

The fast bowler suffered a side strain in Australia's loss to New Zealand on February 28, when he took 2-38.

Clarke said: "He's not playing, not available for selection from the information I've just received for tomorrow's game."

Marsh appeared to hurt himself during Australia's 275-run thrashing of Afghanistan in Perth on Wednesday.

Clarke said the all-rounder had suffered from foot pain, but the 23-year-old insisted he was ready to go.

"I think he had some foot pain. He told me on the field it was his boot, so I assumed it was something to do with the foot," Clarke said.

"But as you've seen today, he's batted, he's bowled, he's done his fielding. I asked him how he was feeling when I walked off from my first bat, and he said, 'I'm flying, I'm ready to go'."

Much has been made about Shane Watson's axing for the win over Afghanistan, with the out-of-form all-rounder dropped for that clash.

Clarke believes Watson has a role to play, even if it is away from his regular position at number three.

"I think he can bat anywhere. I think he's shown that at the top of the order he's been extremely successful," he said.

"He averages over 40 in one-day cricket. I think he's striking it about 90, as well, his strike rate.

"Yeah, I think he's skilful enough to bat anywhere in the order, but I think he's shown that he loves batting at the top in all forms of the game."