The new year has begun chaotically for India, with the afterglow of a series-levelling win at the MCG giving way to concerns relating to life in biosecure bubbles. While there is no official word from the team yet, there are reports suggesting they are unwilling to play the fourth Test in Brisbane if that means a strict hotel quarantine. There is also the issue of five players having to go into isolation as a precaution following a suspected bubble breach.

With all members of the squad having cleared Covid-19 tests since then, however, it is assumed that India will have a full squad to choose from for the third Test at the SCG, which begins on Thursday. In that case, they will have two major selection calls to make, with Umesh Yadav out injured, and Rohit Sharma back in contention.

Where will Rohit Sharma bat?

It's been more than a year since Sharma last played Test cricket, with injuries ruling him out of India's tour of New Zealand early last year and the first two Tests of this Border-Gavaskar series. Given the time that's elapsed since then, you can be forgiven if you forgot what he did in his last season in whites, when he opened for the first time and rattled off scores of 176, 127, 14, 212, 6 and 21 in home series against South Africa and Bangladesh.

Those numbers warrant an immediate return, and Sharma's promotion to Test vice-captaincy suggests he will do just that, but where will he bat? With Mayank Agarwal struggling for form and seemingly beset by technical issues, a straight swap at the top of the order seems the most straightforward solution.

Sharma, though, is yet to open in an away Test, and hasn't had any match practice on this tour, so there could be a case for India to ease him back into action rather than throw him into a new-ball battle straightaway, against Mitchell Starc, Pat Cummins, and Josh Hazlewood.

One way to do this might be for India to replicate what they did at the MCG during their 2018-19 tour, and move Hanuma Vihari up to open. On this tour so far, Vihari has looked solid and organised - particularly in his only innings at the MCG where he faced 66 balls and spent an hour-and-a-half at the crease - but has only managed a top score of 21 in three innings.

Vihari's defensive technique and ability to absorb pressure could come in handy at the top of the order. In that 2018 Boxing Day Test, Vihari only made 8 and 13, but spent a combined 133 minutes at the crease over the two innings, and earned generous praise from Virat Kohli for his efforts. Sharma, meanwhile, batted at No. 6 and scored an unbeaten 63.

*With KL Rahul ruled out with a sprained wrist, India have lost out on another potential combination. This would have had Rahul open alongside Shubman Gill, with Sharma moving into the middle order. Rahul hasn't played Test cricket since the 2019 tour of the West Indies, but he has played five Tests in Australia and scored a hundred, back in his debut series in 2014-15. That hundred, incidentally, came at the SCG.

This combination could have allowed India to go back to six specialist batsmen, if needed. They will now have to retain Agarwal or bring back Prithvi Shaw in order to do so. Given that their win at the MCG was achieved with five bowlers, however, that option seems unlikely.

Who replaces Umesh Yadav?

If India play six batsmen, they might end up with a similar combination to the one they played at the SCG in 2018-19, with two fast bowlers and two spinners. R Ashwin wasn't available then, so India went in with Kuldeep Yadav partnering Ravindra Jadeja in the spin attack. Kuldeep picked up a maiden five-wicket haul that was instrumental in making Australia follow on, and India may well have won that Test if rain hadn't intervened.

Back then, however, their two fast bowlers were Jasprit Bumrah and Mohammed Shami. Now, India are without three of their most experienced quicks in Shami, Ishant Sharma and Umesh, and playing only two fast bowlers would be a risk, given that one of them will be Mohammed Siraj, who has only played one Test.

Of the three candidates to partner Bumrah and Siraj, Navdeep Saini is the only one who was part of India's original Test squad, and the only one to feature in either of the two warm-up games before the Test series. This should make him the leading candidate for the role.

The other two options are Shardul Thakur and T Natarajan. Thakur has only played one Test - he bowled just 10 balls before injury cut his debut short - but has the most first-class experience of the three candidates, with 62 matches to Saini's 46 and Natarajan's 20. Their records in the format are similar, with averages ranging from 27.03 (Natarajan) to 28.55 (Thakur).

In the end, the call could come down to conditions. Saini is the quickest of the three, and hits the deck the hardest, while Thakur is a fast-medium swing bowler who brings useful batting ability in the lower order. Natarajan would be the most left-field option, considering his inexperience, but as a left-armer he offers a point of difference that might tempt India if he has shown them enough evidence of his longer-format skills in the nets.

*GMT 0430 This article was amended following the news of KL Rahul's injury.

Karthik Krishnaswamy is a senior sub-editor at ESPNcricinfo