Shane Watson has ridden the ups and downs of international cricket like few others.

Injury setbacks and reinvention.

Finding form, losing form and never managing to shake the scorn.

Bowling allrounder then batting allrounder, repeatedly shuffling up and down the order.

Test suspension then Test captaincy – that was in the space of a week.

Losing his place in Australia’s World Cup side, winning an instant recall then bear-hugging Steve Smith when the MCG final was won.

The divisive 34-year-old adopted Bobby McFerrin’s mantra long ago.

And that’s exactly how Watson will approach Australia’s final Ashes tune-up, despite knowing a poor showing could mean he is dropped for the series opener in Cardiff.

“I’m well past worrying about where things are at. I’m just incredibly happy to be here,” he said.

The axe would sting for many reasons – this is Watson’s third Ashes tour and he admits winning the showpiece series in England is the only achievement missing from an impressive CV.

Mitch Marsh is viewed as Watson’s long-term replacement, so his stop-start Test career will be nearing its end should selectors opt for change on July 8.

Watson put on a 153-run stand with Marsh in Canterbury last Saturday, crafting a score of 81 as his understudy went berserk with the bat.

“It’s great to be able to see Mitch bat the way he did … he’s a powerful young man,” Watson said of the 23-year-old, who smacked an eye-catching century off 93 balls in Australia’s opening tour game.

“I was just going out there trying to score some runs, spend some time in the middle.

“Being in and around these situations before, I know you can’t worry.”

Coach Darren Lehmann admitted the allrounder selection showdown was “tight”, with both men given the chance to shine against Essex in the four-day clash that starts on Wednesday at 8pm AEST.

Watson was unable to bowl last week and knows he must roll the arm over in Chelmsford to be any chance of playing in Wales.

“It was more just trying to manage the body as well as we can,” he said of being put on restricted duties against Kent.

Settling on an allrounder is just one piece of the puzzle that Lehmann and chief selector Rod Marsh will put together this week.

Opener Chris Rogers missed both Tests against the West Indies due to concussion, with understudy Shaun Marsh scoring a century in Canterbury last week.

Shaun Marsh has been rested from this week’s match, leaving Rogers to open alongside David Warner.

Ryan Harris will be looking to strengthen his case for a Test recall with a bag of wickets against Essex.

The veteran paceman faces stiff competition given the form of Mitchell Starc and Josh Hazlewood, who both return to the attack in Chelmsford after being rested last week.

“He’s obviously got a great Test record and probably even better against the Poms,” Hazlewood said of Harris.

“We know it’s going to be a tough decision.

“This is probably going to be a pretty important game this week here in Essex for Starcy and myself to put some more numbers on the board.”