Former Australia captain Ricky Ponting says a fit Usman Khawaja should return to the Test XI for the Boxing Day Test against the West Indies.

Khawaja has missed the past two Test matches with a strained hamstring he sustained in the second Test against New Zealand in Perth, and will sit out Thursday's KFC Big Bash League opener against Sydney Sixers at Spotless Stadium.

That leaves only one match, the Thunder's clash against Melbourne Stars at the MCG on December 20, to prove his fitness ahead of Boxing Day six days later.

As for who would make way for Khawaja, Ponting says it has to be Australia's form batsman in the past two Test innings stretching back to the pink ball run chase in Adelaide.

"I think Usman (Khawaja) has to come straight back into the side and unfortunately I think it's Shaun (Marsh) that has to go back out," Ponting said a Pontiong Foundation event today.

"The bottom line is Khawaja was in the best XI at the start of summer.

"He played beautifully when he had his opportunity."

WATCH: Khawaja cracks 174 in Brisbane

Khawaja scored two Test centuries in as many Tests to start the summer, but his injury opened the door for Marsh to return to the team and capitalise on his opportunity.

The 32-year-old scored a match-winning 49 in the second innings in Adelaide before combining with Adam Voges to post 182 in the world-record fourth-wicket stand of 449 against the West Indies last week.

Marsh's strong form has created a dilemma Bupa Support Staff Head Coach Darren Lehmann is all too aware of, and says Khawaja's fitness is the first question that has to be answered before the national selectors sit down and decide the playing XI for Boxing Day.

"Usman's first got to be fit. If he's not fit he won't play, there's no doubt about that," Lehmann told cricket.com.au's Stumps show.

"We've got to make sure he's playing BBL to get some sort of match fitness and see how the strain of the hamstring is and then when we get him in on the 23rd (December) we'll have a look at him and see whether he's available to play."

WATCH: Marsh makes Test best 182

Also missing from Thursday's Sydney Smash will be Australia captain Steve Smith.

The prolific right-hander aggravated his right knee and picked up a minor strain to his right hip flexor in the innings and 212-run win over the Windies in Hobart, but is in no doubt for Boxing Day or the New Year's Test in Sydney.

Lehmann expects Smith to play on through the rest of the summer, but will listen to Cricket Australia's medical staff before making a call on his captain's fitness should he need a break.

"He keeps telling me he is 26 but I saw him run today (day three in Hobart) and he was running like he was about 36," Lehmann said after the Hobart Test.

"The pressure of captaincy is quite large. We have to look at that but we get a decent break now with two weeks off. He is not playing the BBL, so he gets a good two-week break.

"The ODIs are pretty important to us and then the T20 World Cup so I can't see him getting a break until probably the end of the summer, unless we play really well or the niggles get worse and we have to rest him.

"I'm no medical expert but [rest] is what they are saying.

"They will say what he can or can't do and if I disagree with it he plays and if I don't he might not play."

WATCH: Stumps with Boof and Patto