The 35-year-old Queenslander was ruled out of the ongoing Essex tour match and is now racing to be fit for the Ashes opener in Cardiff next week.

"We pulled him out because he's sore, he's going to get some scans done and we'll have a better idea in a day or two," Australia coach Darren Lehmann said.

A proven performer on English pitches, Harris was rested for the World Cup and missed the West Indies tour to stay home for the birth of his first child. He took a couple of wickets in the first tour match against Kent but admitted his right knee, which he had major surgery on last year, had bothered him.

With fellow pacemen Mitchell Johnson, Mitchell Starc and Josh Hazlewood all bowling well, selectors are unlikely to risk Harris given his injury history and his usual need to ease his battle-scarred body gently into a series.

Selectors may also be spared the difficult decision of picking an all-rounder, with Mitchell Marsh plundering 136 off Essex's bowlers at Chelmsford on Wednesday. The century was the impressive 23-year-old's second from the warmup matches, placing huge pressure on Shane Watson.

Watson, long the incumbent, hardly disgraced himself with the bat, scoring 52 before being bowled by former Netherlands international Ryan ten Doeschate.

But the 34-year-old's second half-century of the tour was a reminder of his record of failing to convert starts into big scores and he is likely to need a fine bowling performance over the next three days in Chelmsford to hold onto his place.

Australia, who won the last Ashes 5-0 on home soil, are bidding for their first series win in England since 2001. The first Test starts in Cardiff on July 8.

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