CHELMSFORD: Ryan Harris's participation in this Ashes series remains under a cloud after the veteran paceman was sent to London for a second round of scans on his knee on Friday.

As Australia's batsmen endured a tough outing on day three of the tour match against Essex there was increasing doubt about the part Harris might play over the next six weeks.

Results of scans on a painful knee that has troubled him since last week's practice game against Kent were due to be made public on Friday, but instead Australian medicos opted for to have more done at a clinic in London.

There was a further hiccup with Shaun Marsh hit in the hand by a ball from Mitchell Johnson as the pair, not playing against Essex, trained in the morning. Marsh was left with a split fingernail. The chief fitness concern, though, remains with Harris, who while hard pressed to squeeze Johnson, Mitchell Starc or Josh Hazlewood out of the XI for the first Test would be a major loss for the squad if he was to be ruled out of a significant portion of the series or, in the worst-case scenario, scratched for the campaign and sent home.

"I think he's struggling (to make the first Test)," said Michael Clarke, who top-scored with 77. "Without him playing this tour game I don't think he's got enough match practice under his belt to probably warrant playing that first Test now.

"We'll obviously find out more tomorrow about where he sits but my goal is to give Ryano every opportunity. He's done an amazing job every time he's played for Australia. I love having him in the team and I'd love to see him get right and play a part."

In Harris's stead a red-hot Starc (6-51) made short work of finishing off Essex's first innings for 414 on Friday but Australia's batsmen were not as convincing on a pitch that became increasing difficult to bat on in the afternoon.

The Australians, who wore black armbands in honour of slain Adelaide Crows coach Phil Walsh, are 8-212 in their second dig and still lead by 360 with a day to go here, but only Clarke faced more than 60 balls.

The captain was more positive. "I think this preparation has been outstanding," he said. "It's been nice for guys individually to perform and fight for a place in the XI. And we won in Kent, which is great, and that's our goal here as well. That's probably most important for me as much as I want guys to perform individually I'd love us to win these two games leading up to the first Test."

Clarke was beaten trying to cut Essex's left-arm spinner Aron Nijjar, with the 20-year-old bowling him with a low ball that didn't turn.

Nijjar also trapped Adam Voges lbw for one while Shane Watson was also adjudged leg before, for six, when he missed a Ryan ten Doeschate full toss.

That left Mitchell Marsh to ramp up his case to play instead of Watson in Cardiff and while he added 37 to his first-innings 169 he slumped down and swung his bat in disgust when he was dragged the ball into his stumps trying to hit a back-foot drive off Essex seamer Matt Salisbury after tea.

Salisbury also had a driving Chris Rogers out to a nick on 32, while David Warner clipped opening bowler Jamie Porter onto his stumps on four.