Khawaja will see a knee surgeon and consider his options upon returning to Australia.
Khawaja has become the most senior batsman in a heavily depleted top six following the suspensions handed to Steve Smith and David Warner.
"Similarly, we'll just be assessing him in coming days, see how he pulls up tomorrow from spending all that time out there". It's disappointing for him but fingers crossed he gets some good news tonight. He challenged our defence and was too good for us. "We know as a batting group and as a team we're certainly a long way off the finished product, and we've got some work to do".
Get breaking news alerts. Tonight once he's got the scan and we know more that'll determine from the doctor's point of view what he can and can't do.
Australia's Usman Khawaja, who was off the field all of Day 3 during Australia's second Test against Pakistan in Abu Dhabi, has a meniscal tear, which might require surgery.
In the wake of Khawaja's career-defining double of 85 and 141 to save Australia's blushes in Dubai, the gulf left when he can not make runs was demonstrated when his early dismissal on the first evening here led to an inadequate first-innings tally of 145 that effectively surrendered any chance of victory in the match to Pakistan. Siddle, so effective in the Big Bash League for the tournament-winning Adelaide Strikers last season, will be kept in the Twenty20 squad as cover.
Tim Paine delivered a damning assessment of Australia's batting frailties and said the side "wasn't up for it" after Pakistan wrapped up the series with a crushing victory in Abu Dhabi. "Over here one of the things our bowlers talked about was building pressure from both ends, and that's what I think they did really well together, and when Sarfraz [Ahmed] used them together, there was a lot of pressure at both ends, and when you can create that pressure mistakes happen, and that's what they did really well". Physically and mentally, it's so draining. We had some momentum from the first Test, started really well here and then from 5 for 57 it went a bit, to be honest, all over the field. "They're all important Test matches". Remarkably this is not Marsh's poorest series in Tests, after he managed just 17 at 2.83 against India in 2011-12.