Adelaide - Australia captain Michael Clarke suffered a lower back injury and was forced to retire hurt before tea on the opening day of the first Test against India in Adelaide on Tuesday.
The injury puts a question mark over his participation in the remaining three matches of the series as well as Clarke's ability to lead Australia into the 50-over World Cup early next year.
The 33-year-old was only playing after coming through a fitness test on a third hamstring strain in three months, problems which are related to his long-term degenerative back injury.
A Cricket Australia spokeswoman said Clarke had hurt his lower back when batting at the Adelaide Oval and it was causing him "considerable pain".
She added that he had left the ground for treatment.
Clarke had made 60 not out when he twisted to avoid a short ball from Ishant Sharma. He tried to stretch out the injury with medical staff but trudged off minutes later with Australia on 206-2.
Clarke had appeared in full control against India's bowlers and his retirement subdued the crowd of over 20 000.
He has missed just one of Australia's 40 tests since he assumed the captaincy in 2011 but may come in for some flak for putting sentiment ahead of team interests by playing in Adelaide.
Clarke has spent much of the last two weeks leading the nation in mourning for his friend and former team-mate Phillip Hughes, who died after being struck on the back of the head by the ball in a domestic match.
Hughes's memory was being honoured throughout the match at the Adelaide Oval, where the lefthanded batsman played his state cricket for South Australia for the last couple of years.
Team physiotherapist Alex Kountouris said last month that Clarke risked breaking down with another hamstring strain on his first run-out after his return from injury regardless of how long he was rested.