Australia's Pat Cummins has been told his slower balls are too predictable and he needs to go back to using his raw pace as his biggest weapon despite the slow nature of Sri Lanka's pitches.

The 19-year-old bowled one of the best overs of the World Twenty20 tournament in Australia's Super Eights match against India on September 28, taking the key wicket of Virat Kohli by producing two good short balls in a row then whizzing a bouncer past new batsman Yuvraj Singh's nose.

However the Penrith product has gone off the boil in his past two games, conceding 0-33 against South Africa and 1-42 on Tuesday night as Pakistan claimed a 32-run win.

Skipper George Bailey's side face West Indies in Friday's knockout semi-final and if Australia reach Sunday's final they'll take on a subcontinent team less keen on facing pace -- either Sri Lanka or Pakistan.

"He got a touch-up against the West Indies (1-41 off four overs on September 22) and a little bit last night but he still plays a massive role for us," Australia coach Mickey Arthur said on Wednesday.

"If the wickets are starting to show a little bit of inconsistent bounce at that pace it's tough. He hits the deck hard."

Arthur feels Cummins has a good grasp of the tactics required in T20 International cricket, but some fine-tuning is required.

"I do think he got it a little bit wrong last night and I've already had a chat with him," Arthur said.

"He became a little bit too predictable with his slower balls.

"His comment was that he thought his slowest balls were the toughest to hit because they were really gripping.

"I said to him 'you're a guy that bowls 150 kilometres an hour. Why would you want to bowl that many slower balls because the batter would far prefer to face a slower ball from you than your quicker one?'.

"The subcontinent teams don't want to see Pat Cummins hit the deck at 150 kilometres an hour.

"Against the West Indies, he might just have mix it up just a little bit more."