The powerful all-rounder will have scans later in the day on what he believes may be a fascial tear, before discussing the results with Cricket Australia's medical staff and working out how best to prepare for the Brisbane Test, which starts on November 21.
"It's not too bad," Watson told reporters at Sydney airport.
"I've had a few niggles like this even over the last eight or nine months, so hopefully it won't be too bad at all or put me out for too long.
"Being here, it'll give me a week or two to be able to hopefully freshen up and (be) ready to go for the first Test."
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Asked if he had any doubts about whether he would be involved in the series opener, Watson said: "I'd never say 'no doubt' but I've been able to get on top of this sort of thing over the last eight or nine months with a few niggles that I had even throughout the (July-August) Ashes as well.
"So I'm very confident that things should work out OK over the next couple of days and the results will be what I think they are and there shouldn't be any problems at all."
He said while international cricket was "not an ideal world", he was happy to play as much as possible.
"We certainly aren't underdone for cricket, that's for sure. For a majority of us, we've been playing for quite a while, so there should be no excuses for us being rusty at all," he said.
Hamstring injuries have been common for the former vice-captain -- he missed the 2006-07 Ashes campaign with one -- and there has always been a question over how to balance his workload as an all-rounder.