It has been almost 20 years since Australia's cricketers have been stung by Sri Lanka at a Cricket World Cup.

It is a trend Michael Clarke's men are expected to continue at the SCG on Sunday, but the captain knows that it will not be easy to achieve victory.

"They've got some world-class players. They're going to be as tough as any team," Clarke said.

"If they play their best, they're always a tough team to beat.

"They've shown throughout World Cups that they're always going to be there or thereabouts. They seem to like World Cups.

"They're in really good form and playing well."

Sri Lanka defeated Australia in the 1996 World Cup final, but it has been one-way traffic at tournaments since then.

Neither team has yet finalised their XI for the all-important clash in Sydney, with selectors wanting to assess the pitch just before play.

The loser of Sunday's fixture will almost certainly face South Africa in a quarter-final.

"Regardless who you play in the quarter-final, you're up for a tough match," Clarke said.

"Who we play against is irrelevant. We just need to continue to win every game we play."

Pat Cummins will miss a second game due to the side injury he suffered in Auckland, however the paceman is expected to be fit for the team's final pool match against Scotland in Hobart.

Sri Lanka skipper Angelo Mathews feels his side could do some damage over the next three weeks, having shown much improvement since losing to New Zealand in their tournament opener.

"Coming into the World Cup no one really gave us a chance," Mathews said.

"We had a pretty poor series against New Zealand. We didn't play that good cricket.

"But I think we are peaking and I think we're peaking at the right time."
(AAP)