The 34-year-old quick underwent surgery on his knee in March after battling through the pain barrier to see his country to a dramatic series victory over South Africa in Cape Town.
McDermott said Harris was recovering well but would not be rushed back with a domestic summer against India, the one-day World Cup and a 2015 Ashes series on the agenda.
"He's definitely touch and go for Dubai, we've just got to see how his knee goes over the next few months," he told reporters.
There is also serious doubt over fellow fast bowler James Pattinson after he suffered a recurrence of the back problems that have plagued his career.
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Pattinson, 24, missed most of the Australian domestic summer but recovered to star in Australia's third Test triumph over South Africa in Cape Town in early March.
He has not bowled since with reports that he has suffered further stress to his lower back.
"Patto does bowl fast ... So we've got to make sure we get him right and take our time to bring him back nice and slowly."
Australia are due to play two Tests, four one-day internationals and a Twenty20 against Pakistan in the UAE from October 4.