Australian team physio Alex Kountouris attended to Hayden in the evening and the Queenslander is likely to face a fitness test on Sunday.

Hayden sustained the injury during the tumultuous second Test in Sydney but Nielsen is hoping against hopes that the towering opener would recuperate well in time to play the third Test starting here on Wednesday.

"Speaking to him this morning (Saturday), he is feeling like he is just ahead of 50-50. He really hasn't done much over the last couple of days," Nielsen said.

The 36-year-old Hayden has been fit enough throughout his career not to miss a Test and in case he makes it to the third Test, he would be playing his 87th straight match with the Baggy Green.

"There are four or five days to go. He needs to get up and start batting and catching over the next couple of days. If that doesn't hold him back too much, he'll be fine," an optimistic Nielsen said.

In case Hayden sits out, Australia will announce a replacement on Monday.

"Until he runs around, trains and plays some cricket for us, it is hard to make a decision," Nielsen said.

"Over the next 24 to 48 hours, he'll get a chance to have a training run and see how he pulls up. That will give us the real indication where he is at," he added.

If the hamstring injury keeps Hayden out, it would be a toss up between uncapped West Australian opener Chris Rogers, who scored 60 and 17 against India in the warm-up match, and New South Wales captain Simon Katich.

With the WACA pitch promising a lot for the fast bowlers, Australia might unleash a four-pronged pace attack on the visitors, Nielsen hinted.

In such a case, Brad Hogg would have to pave way for slinger Shaun Tait.

"He's (Tait) very much at the forefront. But we haven't seen the wicket yet. We'll get a good chance to look at the conditions tomorrow (Sunday) and make sure we pick the best side we can for the game coming up and the conditions the WACA presents for us," Nielsen said.

"If we turn up and it looks green, fast and bouncy, Tait will probably have his nose in front.