Ishant Sharma and Rohit Sharma have been ruled out of the first two matches of the upcoming four-Test series in Australia and their hopes of taking part in the last two Tests hinges on swift and decisive action from the BCCI, ESPNcricinfo has learnt.

To be in contention for the third Test, Ishant, who has regained bowling fitness but needs four weeks of workload to be ready for the rigours of Test-match play, will have to board a plane almost immediately.

The 14-day hard quarantine rule in Australia means he can start training only after two weeks; add another four weeks of preparatory training, and he can only be match-ready for the third Test, starting on January 7 in Sydney.

Rohit, who suffered a hamstring tear during the IPL, is understood to be a while away from full fitness. He can be cleared travel only in the second week of December and will need two weeks of further rehabilitation after which a final assessment can be made. According to a BCCI functionary, Rohit would have had a better chance of featuring in the Test series had he flown directly to Australia with the other squad members from the UAE.

Even if he flies out on the earliest possible date, which is December 8, he would have to serve a 14-day hard quarantine, which will keep him out of training until at least December 22.

Ishant's bowling workload has steadily increased over the past week after he regained full fitness at the National Cricket Academy in Bengaluru, where he has been training for close to a month since returning early from the IPL with an abdominal muscle tear. However, ESPNcricinfo understands there are concerns over his match fitness, which can only be ascertained once he's in a position to bowl at least 20 overs in a day.

"If there is a T20 game and he needs to just bowl four overs, Ishant is good to go immediately, but for him to get back to Test-match fitness, he needs four weeks of proper bowling still," a BCCI source said.

As such, even if Ishant and Rohit were to fly out in a day or two, the hard quarantine would mean each of them needing to isolate himself in his hotel room for 14 days. This will mean neither is able to take part in the two warm-up games that precede the first Test in Adelaide, which begins on December 17.

The 32-member India contingent has begun training in Sydney while in quarantine since they flew over directly from one biosecure bubble in the UAE - after the completion of the IPL - to another. Such concessions can't be afforded to Rohit and Ishant upon arrival, since they aren't in a biosecure bubble at the NCA where they are currently training.

If Rohit is ruled out, the selectors could look at adding Shreyas Iyer - who is already part of the white-ball squads - to the Test squad as a reserve batsman. In 54 first-class games, Iyer has aggregated 4592 runs at an average of 52.18. He has 12 centuries and 23 half-centuries, and has already been part of India's red-ball squad - when he was called up as cover for the injured Virat Kohli during the 2016-17 home series against Australia - but is yet to make his Test debut.

As for the fast bowling, India already have Jasprit Bumrah, Umesh Yadav, Mohammed Shami and Mohammed Siraj in their Test squad. The contingent also has three reserve bowlers in Kartik Tyagi, Kamlesh Nagarkoti and Ishan Porel to pick from, if needed.