Three-time World Cup winner Ricky Ponting says the axing of Shane Watson leaves Australia's batting line-up dangerously exposed heading into the business end of this World Cup.

Watson was dropped for Australia's match against Afghanistan on Wednesday, with Steve Smith moving up the order to replace the allrounder at first drop and James Faulkner coming back into the side to bat at No.7.

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The new-look batting line-up flourished against the Associate nation in Perth, compiling 6-417 with opener David Warner, Smith and Glenn Maxwell the stand-out performers.

But Ponting warns a middle order consisting of Maxwell at No.5, Mitchell Marsh at No.6 and Faulkner at No.7 could be exposed against the better nations later in the tournament.

"Steve Smith is a brilliant batsman and there is no problem with him batting at No.3, but with the team they had against Afghanistan you are asking for problems," Ponting wrote in The Australian.

"If you lose early wickets you have Maxwell coming in at No.5 and I am not comfortable with that.

"I think it would make the selectors nervous too.

"That's nothing against Maxwell. He is a terrific player but he is better in certain roles and positions.

"If the team is 3-20 there is a lot of pressure on him and he has to play a different role.

"Maxwell is an X-factor player and I just don’t know about him coming in at that spot, especially with Faulkner following.

"Look, they are all terrific players and exciting talents and we have seen them save the side on occasions when the pressure has been put on them, but you can’t bank on that."

Watson has conceded he only has himself to blame for his axing having passed 50 once in his past 12 ODI innings.

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While the 33-year-old has been out of form, his overall career record of nine ODI centuries and an average in excess of 40 underlines his ability at the top of the order.

His output with the ball has also been down in recent times; he hasn't taken a wicket in the past six matches in which he's bowled and hasn't taken two wickets or more in an innings since October 2013.

But with a career record that includes 164 wickets at an economy rate of fewer than five runs an over, Ponting believes Watson is a better option than Marsh as one of three allrounders in the side.

Ponting also suggested a lack of continuity may be behind Watson's drop in form.

The allrounder missed Australia's ODI tours of Zimbabwe and the UAE last year due to a calf injury and he also missed three of Australia's five matches in the Carlton Mid ODI Tri-Series that preceded the World Cup.

Ponting says the XI that cruised to victory over Afghanistan could be exposed in the crucial clash against Sri Lanka at the SCG on Sunday, the winner of which will likely finish second in Pool A and avoid a quarter-final against the dangerous South Africa.

And believes Watson is more than capable of again proving his worth to selectors.

"Deep down he knows he is good enough and the selectors do too," Ponting wrote of Watson.

"I hope he gets a chance to prove it and I bet he is spending a lot of time in the nets at the moment. People don’t realise how determined Watto is.

"I can imagine they tossed a lot of things around in the selection meeting and would have agonised over the decision.

"I think Watson brings more to the team than Marsh. The young bloke will prove to be a very good cricketer.

"I thought that against Afghanistan they would play two quicks and leave Watson in and I was very surprised when they left him out.

"That is not an option, however, against good batting line-ups and Sri Lanka are that."