The off-spinner, who can also bat, is set to leave for Australia on Tuesday, two days before the start of the Boxing Day Test in Melbourne, reported India Today.
Ashwin, who announced his retirement from international cricket after the third Test of the series, decided to return home.
The series is currently levelled 1-1.
Kotian has played 31 First-class games for India.
He has scalped 101 wickets in his career so far.
He will join Washington Sundar and Ravindra Jadeja to strengthen the Indian spin attack.