India spinner Ravichandran Ashwin has been ruled out of the fourth and final Test against Australia due to an ongoing abdominal issue.

Veteran Ashwin was hoping to feature in Sydney on Thursday, having missed the past two Tests with a side strain sustained in Adelaide, where he finished with figures of 6-149.

However, the 32-year-old failed a fitness test and was ruled out by captain Virat Kohli, whose team have already retained the Border-Gavaskar Trophy as they seek to become the first India side to win a series in Australia.

"It's unfortunate that he's had two niggles that are quite similar in the last couple of away tours," Kohli told reporters at the SCG on Wednesday. "It's something he will focus on to correct.

"The physio and trainer have spoken to him about what he has to do. He's very important in Test cricket, he's a vital part of the team. We need him to be 100 per cent fit.

"He's very disappointed he hasn't recovered in time."

A full house at training? Sample the SCG at the moment as #TeamIndia train ahead of the Final Test against Australia #AUSvIND pic.twitter.com/ZwZSHiPQAN

— BCCI (@BCCI) January 1, 2019

Fellow spinner Ravindra Jadeja is expected to stay in the side following his exploits during the Boxing Day Test in Melbourne, where he claimed five wickets in the 137-run victory.