India team director Ravi Shastri has admitted that he was surprised by MS Dhoni's decision to announce his retirement from Test cricket after the draw with Australia in Melbourne.

Dhoni stepped away from the longest format of the game after another series defeat was confirmed with a match to spare, and Shastri believes that no-one could have seen the decision coming.

"It came like a bolt from the blue. Not till after he returned from the post-match presentation did I come to know when he had a quick word with me, then the players. I understand he had not even spoken to his family about it," India's former all-rounder told reporters.

"It was an unexpected decision no doubt, but a courageous one. In my esteem Dhoni has gone up by miles. He hasn't waited to complete 100 Tests and all such pointless statistical stuff. He didn't want any farewell fanfare. That shows his character. He's different and quite remarkable."

Virat Kohli will lead India in the fourth Test, which begins in Sydney on Tuesday.