Mathew Leckie looks likely to lead the line, while Oliver Bozanic could come in for the doubtful Mark Bresciano. Spain have their own headaches over under-performing players
Will Vicente Del Bosque persist with captain and stalwart Iker Casillas? The Real Madrid goalkeeper by his own admission let La Roja down in the 5-1 loss to the Netherlands, although his defenders ought to shoulder plenty of the blame there too. He didn't cover himself in glory against Chile either. But while the clamour to drop him continues to grow, what purpose would humiliating a great servant of club and country serve in a dead rubber against Australia?
At the other end, Mat Ryan hasn't had an opportunity to perform the heroics that earned him the number one shirt for the Socceroos. The Club Brugge custodian, tenuously linked with Casillas' Madrid ahead of the tournament, might feel he could have done better for Memphis Depay's winning goal in Australia's 3-2 loss to the Netherlands and will be determined to make his mark against Spain.
2. Who will replace Tim Cahill?
With Australia's goal-scoring talisman suspended, the obvious solution appears to be moving Mathew Leckie to the centre and bringing in Ben Halloran (or Dario Vidosic) to start on the right. Leckie's pace and physicality have worried both Chile and the Dutch, meaning he could be capable of terrorising a shaky Spanish backline.
By the same token, Adam Taggart's pace and poacher's instinct could also be of interest against Sergio Ramos and Javi Martinez/Gerard Pique. But the diminutive Jets man is more likely to be kept in reserve as an impact player off the bench.
3. Matt McKay to keep his place
Mark Milligan is reportedly set to be fit after overcoming the hamstring strain that kept him out of the Netherlands game. However, his replacement, Brisbane Roar's McKay, will surely retain his spot in the starting XI after excelling in the Porto Alegre thriller. The A-League championship winner linked up well with holding midfield colleague Mile Jedinak, shielded the back four and recycled possession when required but also got forward to good effect, almost setting up a goal for the Socceroos. It would be harsh indeed to relegate him to the bench.
4. Will Diego Costa get the chop?
The Brazilian-born striker, a naturalised Spanish citizen, has been a huge disappointment playing for La Roja in the country of his birth. Carrying a hamstring problem into the tournament, the Atletico Madrid man has been anonymous up front and appears set to pose far less of a threat to Alex Wilkinson and Matthew Spiranovic than Robin van Persie and Alexis Sanchez did. Even if Del Bosque axes him in favour of Fernando Torres and David Villa, the Socceroo centre-backs appear to have their best chance of keeping the opposition forwards quiet.
5. Is Mark Bresciano fit to play?
Nursing a flare up of a long-term back problem going into the tournament, Bresciano managed 78 influential minutes against Chile but only 50 in the Netherlands game. Oliver Bozanic was a revelation off the bench in his place, keeping the ball, winning it back and demonstrating a football intelligence that belied his lack of international experience. Postecoglou could be tempted to start the Luzern man in a match with nothing to lose and everything to gain.