Vice-captain Ajinkya Rahana will have to step-up in Virat Kohli's absence for the last three Tests.
Rahane, the middle-order mainstay and Kohli's deputy, will be the one at the helm for the majority of the forthcoming series as the regular captain returns home on paternity leave after the first Test in Adelaide.
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"Virat's departure from the team is a huge blow to the Indian campaign in Australia," Buchanan told ANI. "They will miss his enthusiasm, his competitiveness, his belief in what they can do as a team. On top of this, they will be missing one of the finest batsmen in world cricket."
"I do not have any insight into Rahane as a leader and a captain. He will not be Kohli, nor should he try to be. His first job will be to score runs, and lead by example this way," he added.
Rahane has previously captained India to victory in a high-pressure series-decider at home against Australians in the 2017 series and also seen India over the line against Afghanistan in two countries maiden Test outing the following year.
But the 32-year-old hasn't had any experience of leading the side abroad yet, a task that will be made tougher by the fact that his own batting hasn't held up that consistently over the last three years.
Buchanan, on a different note, said reaching Australia early because of the quarantine regulations amid COVID-19 pandemic, will help the Indians get accustomed to those conditions as they also play 3 ODIs, 3 T20Is and a couple of warm-up fixtures in the build-up to the Tests.
"Yes, it is always good to be in a foreign country for a while, playing matches before a Test series. Although, this year is different due to COVID. Most players have been in a bio-bubble for some time during IPL and now will continue in that situation while touring Australia."
"I expect many of the Indian players to be feeling the effects of this lockdown/isolation by the time the New Year Test begins which may cause some issues for individuals and the team."
With Ishant Sharma currently undergoing rehab for a side strain at the NCA in Bangalore, Buchanan worries the experienced pacer's potential absence could expose chinks in India's armour, testing the mettle of Umesh Yadav or uncapped Navdeep Saini, Mohammad Siraj as the third paceman alongside Jasprit Bumrah and Mohammad Shami.
"I think the Australian bowling attack of Cummins, Starc, Hazelwood, Pattinson, Neser, Lyons, Swepson look a stronger and more balanced attack than India, especially if Ishant is not available. Playing in Australian conditions, bowlers need experience. Ashwin and Kuldeep will play good support roles and may be a factor in Sydney," he said.
"But India lacks solid backup to Bumrah, Shami, and Yadav. Bumrah is a fine paceman. He has very good durability. I think India needs to use him in such a way that he is as fresh as possible for each Test match," Buchanan added.
The Test series begins on December 17.