Michael Clarke remains in doubt for Australia's must-win clash with host nation India at the Champions Trophy on Sunday.

Clarke, who is suffering from tonsillitis, has returned to light training with the side in the past two days, with Simon Katich on standby should he not pull up.

Katich would move into the middle order for the Australians, with Shane Watson to open alongside vice-captain Adam Gilchrist.

Captain Ricky Ponting said that Clarke's condition had improved after he missed three days of training, but added he would not be fully match fit should he take his spot in the side.

"Michael got through training and did everything he wanted to on Friday," Ponting told The Age. "He has improved fairly dramatically over the last few days but … we'll see how he pulls up."

"He probably won't be 100 percent for the game. We'll keep our fingers crossed and hope that he is, but he's had a week lying around in his hotel room. It's more about just getting acclimatised again, getting back out in the sun and being able to run around a bit."

Meanwhile, injury-ravaged India has suffered another blow ahead of the crucial clash with star batsman Yuvraj Singh ruled out after tearing knee ligaments during training on Saturday.

Singh was playing kho-kho, a running and catching game, when he injured himself, and is expected to be replaced by Mohammad Kaif.

Ponting said the loss of Singh, a nominee for one-day player of the year, swung the match in his side's favour, particularly as his replacement averages just 20 in one-day cricket.

"He has probably been the best one-day player in the past 12 months," Ponting said. "India will miss his batting and probably his fielding too."

The absence of Singh will further test the ranks of the depleted Indians, with paceman Ajit Agarkar already ruled out with a thumb problem, while Munaf Patel has bruising on his wrist.

Patel is expected to play, but Agarkar's spot in the side will be taken by young bowler Shanthakumaran Sreesanth, while Rudra Singh is likely to be omitted for off-spinner Ramesh Powar.