Ashwin, who suffered an abdominal strain on the fourth day of the opening Adelaide Test, trained on Tuesday but has not recovered in time and will miss his third Test in a row.
Left-arm finger-spinner Ravindra Jadeja is expected to stay in the side for the fourth Test beginning Thursday. Australia must win to prevent India, who lead 2-1, claiming a first-ever series triumph Down Under.
“It’s unfortunate that he’s had two niggles that are quite similar in the last two away tours,” said skipper Virat Kohli.
“He’s very important for sure. In Test cricket he’s a vital part of this team and we wanted him to be 100 percent fit for a longer period to that he can come back to us in the Test format.
He is very disappointed that he’s not able to recover in time.
India will need to make at least one change to the team that won in Melbourne with middle-order batsman Rohit Sharma, who hit a gritty 63 in the first innings, jetting back to Mumbai after his wife gave birth to a daughter.