Indian captain Jasprit Bumrah was sent for scans after lunch on day two at the SCG.
The superstar quick was on fire early in Australia's batting innings, dismissing both Usman Khawaja and Marnus Labuschagne to put the visitors on top.
However, with the first innings in the balance, Bumrah left the field after bowling just one over following the main break.
FOLLOW LIVE: Australia vs India fifth Test, day two
Jasprit Bumrah grimaces during the SCG Test. Getty
Moments later, the 31-year-old was spotted walking out of the Indian dressing rooms and had already changed out of his playing kit.
"He just bowled that one over after lunch and at that point he decided to leave the ground," Adam Gilchrist said on Fox Cricket.
"It's such a shame and the body language and lack of enthusiasm and voice from India since that moment, it's quite obvious something is amiss here.
"That would be devastating, not just for this Test match but the outcome of this series."
Jasprit Bumrah leaves the SCG with an injury. Fox Cricket
Mystery surrounded the situation as Australia attempted to inch towards the modest total set by the visitors, before footage showed Bumrah getting into a car.
It has been reported he will head for scans on an unspecified injury.
"It's horrible news isn't it? That's a massive moment in this series," Brett Lee said.
Despite his absence, India managed to take a stack of wickets in the second session.
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