Johannesburg, Feb 22 : Australian Vice-Captain Michael Clarke is likely to be ruled out of the first Test match against South Africa due to a serious back injury. The first Test match will start on Thursday.

Admitting the spasms and discomfort, Clarke had a couple of net sessions instead of playing a tour match against South Africa Board President's XI at Senwes Park.

His unavailability for the first Test match would be serious blow for Kangaroos who have lost their number one spot in recent times.

Clarke, who had a lot of inflammation and spasm, said, "I do not know exactly how it happened. I guess it's a sprain. I had a lot of inflammation and spasm. It is improving slowly every day since we arrived here."

The Australian Vice-captain was, however, hopeful to play in the first Test match.

"I am getting plenty of treatment from the physiotherapist. I am working on more batting every day and hopefully I will be able to have a field, have a bit of a run around. I guess, hopefully it continues to improve and I would be able to play in the first Test match," he said.

Clarke, who is also a useful left-arm off spinner, is not thinking about bowling at this point of time.

Clarke was ruled out of limited overs and Twenty20 matches against New Zealand at the end of the international season in Australia with a lower back problem. (ANI)