Cameron Green's condition has improved since Friday but the concussed allrounder is unlikely to be ready in time for the first Test, according to Australia's former team doctor Peter Brukner.
Green suffered a scary head knock while bowling on Friday during a tour game at the SCG.
Jasprit Bumrah bludgeoned the ball back at Green, who walked off the field smiling but was soon substituted out of the match after being diagnosed with concussion.
Australia A doctor Pip Inge noted on Saturday that Green "has shown clinical improvement overnight and is symptomatically better than yesterday".
"He will remain with the Australia A squad where we will continue to monitor him," Inge said.
Green had been building a near-irresistible case to make his Test debut in the series opener between Australia and India, which starts at Adelaide Oval on Thursday.
But the 21-year-old now has scant time to tick the requisite boxes that would allow him to be passed fit for the first Test.
"Green is really cutting it fine," Brukner told ABC Radio.
"Six days (between the blow and the start of the first Test) ... you'd almost rule Green out of the Test match if he has a concussion confirmed.
"The quickest someone can get back from a concussion is five days really.
"But that is if everything goes well, (and) they're waking up the next morning symptom free."
Cricket Australia's concussion protocols dictate a gradual return to play after a head knock, with each day bringing incremental steps.
Green must be free of symptoms for 24 hours before getting the green light to walk laps.
The West Australian would, provided he does not experience symptoms, then be cleared to attempt more rigorous activity.
The final step would be facing express pacemen in the nets.
Green's setback came a day before Will Pucovski was ruled out of the first Test because of a concussion he suffered while batting in a tour game.
"It's really disappointing for those two young guys," Brukner said.
"The most important thing is they recover quickly and can move on with their cricket. Whether that it is in a week or a month."
Brukner added concussion has "become a major problem in cricket".
"It's such a difficult condition to diagnose, manage and determine when it's safe to return," he said.
