Australia have been dealt a blow ahead of the Ashes second Test after captain Michael Clarke was forced to miss a practice session due to an ankle injury.

The 32-year-old, who has a recent history of back problems, struggled through training on Monday although Cricket Australia were quick to play down the severity of his issue after he was seen limping and repeatedly flexing his left ankle.

Clarke was absent from Australia's preparations for the second Test on Tuesday, but Shane Watson insists that there is nothing to worry about.

"Obviously Michael batted beautifully in the first test, so his preparation was always going to be very good anyway," Watson told reporters.

"I know the medical staff and Michael are very confident. It was just giving him a break today and he'll be training flat-out tomorrow, ready to go for Thursday."

The second Test gets underway at the Adelaide Oval on Thursday with Australia holding a 1-0 lead.