The fourth Ashes Test could be headed for a draw, but the series has conjured up some controversy, with Australian commentators accusing England of ball tampering at the MCG.

Umpires Sundaram Ravi and Kumar Dharmasena spoke to England skipper Joe Root after a throw from Stuart Broad in the field bounced short of wicketkeeper Jonny Bairstow.

It's a practice common around the cricket world where the fielder takes a shy at the stumps or the keeper in an effort to scuff the ball on the turf, roughing up a side of the ball in an attempt to produce more swing.

Television cameras then captured bowler James Anderson running his thumb over the quarter-seam of the ball.

Channel Nine commentator Michael Slater said: "You can't get your nail into the ball. That's a no-no."

Co-commentator Shane Warne, taker of 708 Test wickets for Australia, said the footage of Anderson's thumbnail near the quarter-seam would get people talking.

"I'm not sure you are allowed to use your fingernail there," Warne said on Nine's telecast.

"If you are going to touch the ball at all, it's not just shining it, you want to do it right in front of the umpire so they know there is nothing untoward going on."

However, the England team's head of communications Danny Reuben said he was unaware of Root being spoken to by umpires about ball tampering.

Former Australian fast bowler Mitchell Johnson observed on Twitter that England was already procuring reverse swing inside the first 10 overs of Australia's second innings, after the hosts had dismissed the tourists for 491 early on day four, a lead of 164.

It's yet another potential ball tampering saga after last summer saw South Africa captain Faf du Plessis charged for coating the ball with saliva while he had a lolly in his mouth.

Speaking to Cricket Australia, former Test batsman Michael Hussey said Anderson might have explain himself to the match referee.

"It didn't look great, to be honest. There might be a little bit of a 'please explain' there for Jimmy Anderson," Hussey said.

"I know there's a lot of tactics, but there's a bit of a line there that you shouldn't cross in picking the seam of the ball and things like that.

"The English have been throwing the ball into the ground to try and scuff one side up, but that's nothing the Aussies weren't doing either and the umpires are generally on top of that pretty quickly.

"But certainly getting a thumbnail into the ball is against the rules.

"It'll be interesting to see what happens and if anything plays out there."