MELBOURNE - Wicketkeeper Tim Paine has joined pace spearhead Mitchell Starc as a doubt for Australia in the Boxing Day Test against England in Melbourne.

Starc hobbled through Melbourne airport on crutches Friday cushioning a bruised heel but was not yet ready to concede defeat. "It won't be my choice," he told reporters, on his possible selection. Reports said that Starc, who is Australia's leading wicket-taker in the Ashes series with 19, could be ruled out of the fourth Test as soon as Saturday. If Starc is unable to recover in time understudy Jackson Bird is expected to take his place in the XI.

With Australia having already claimed the Ashes, another factor against the left-armer playing in the Boxing Day Test is an upcoming series in South Africa, with selectors keen to pick a healthy Starc in the touring party. Paceman Ryan Harris, who often played in pain throughout a Test career that included Australia's home Ashes success four years ago, knows how much of an impediment a bruised heel can be. "I have had it. They can be quite painful," Harris told radio on Friday. "You can't hide it. You can't change anything -- the way you land or try and get around it."

Reports emerged on Friday that Paine is also no certainty to play in the showpiece Melbourne Cricket Ground Test. Paine, who is averaging 43.33 with the bat and has taken 15 catches and a stumping in the series, did not travel to Melbourne with the rest of his team-mates because of personal reasons. The Daily Telegraph reported that Paine had remained at home in Tasmania after his father-in-law suffered a stroke.

If Paine is unavailable for the MCG Test, selectors have several options to consider. Dropped batsman Peter Handscomb could potentially play as a wicketkeeper, while Cameron Bancroft was behind the stumps for Western Australia during the the early rounds of the domestic Sheffield Shield season.

Smith vows no let-up on bouncers to England's tail: Australia captain Steve Smith says his fast bowlers will continue to bombard England's tailenders with short-pitched deliveries despite claims their beleaguered batsmen deserve more protection from the umpires.

Smith's uncompromising stance comes after former England captain Mike Atherton called on umpires to better enforce the game's laws around bouncers which are designed to shield batsmen down the order. Australia trounced the tourists by an innings and 41 runs in Perth on Monday to reclaim the Ashes and hold an unassailable 3-0 lead with two Tests to play in Melbourne and Sydney.

In the three Tests so far, Australia's pace battery has targeted England's tailenders with short-pitched deliveries. Last man in James Anderson was struck a fearsome blow on the helmet grille by a brutal bouncer from Pat Cummins in Perth which drew criticism from Atherton, writing in The Times. Atherton said he was dismayed by the continued attacks on the England tail, which included six bouncers to Anderson in the last rites of that Test.

But Smith said there would be no let-up in the fourth Test starting in Melbourne on Boxing Day, adding that it was a strategy England would employ themselves if they could. "We obviously had a plan from the start of the series that we were going to bowl a lot of short stuff to those guys, much like we did back in 2013," he told reporters late Thursday. "And no doubt if they have the kind of pace our bowlers could generate they would probably do the same thing."

Former pace spearhead Mitchell Johnson, who put England to the sword in that 2013 home series, said rather than worry about the laws the tourists should just "learn to bat". "Isn't it two short balls in an over? That's the rules. If it's not over their heads or the shoulder restriction, how is it dangerous?," Johnson told Fox Sports. "I don't see the issue with it -- yeah, some guys struggle to hold the bat. But whose fault is that? That's not the fault of the Australian quicks. (England) should be working on their batting."

Another former Australia Test quick Trent Copeland tweeted: "What's missing from this (Atherton) article? "The fact that ENG would do exactly the same IF they were fast enough to do so, and the Aussie lower order players work hard enough at their batting so that it's not an issue. Sorry, but its TEST cricket. Suck it up."