Mitchell Johnson's great fast bowling accomplice Ryan Harris says the Aussie quick would have kept playing if it was not for the tepid state of Australia's Test wickets.

The relentlessly accurate Harris, who retired after picking up a knee injury ahead of this year's Ashes series, was the perfect foil for the intimidating Johnson when the pair led Australia's pace attack.

Harris had spoken to his friend recently and saw no signs he was about to call it quits, but he thinks Johnson's figures of 1 for 157 on a WACA road in the first innings of the second Test may have accelerated the decision.

"I'd known for a while he'd thought about potential retirement," Harris told Grandstand.

"Speaking to earlier in the week, he wanted to keep playing for as long as he could.

Sorry, this video has expired Watch highlights from Mitchell Johnson's career with ball and bat

"There is a period during that Test that he's ether lost the fire or something wasn't right.

"He's made that tough decision. As an elite athlete doing what we did, and what Mitchell did, we though it was the best job in the world and you want to keep doing it forever.

Harris said the prevalence of pitches which heavily favour batsmen over bowlers probably caused Johnson to consider the value in playing on.

"I am sure that was part of his decision making. I am sure there are probably a few other bowlers around thinking the same thing," he said.

"I think the wickets are ridiculously flat, especially when you are playing a home series.

"It would be nice to play conditions that we are probably used to a bit more, with a bit more bounce, and a bit more pace in the wicket."

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"I loved watching him bowl": Harris

Mitchell Johnson in full flight was one of the most thrilling sights in cricket. ( Getty Images: Gareth Copley )

Harris expressed regret that he and other cricket fans would no longer get to watch one of cricket's most exciting spectacles: Johnson in full flight.

"I'm shattered for Mitchell. He's a very good mate of mine, I would have loved to have seen him gone on," Harris said.

"I loved watching him bowl.

"I got to know him about eight or nine years ago. He's just a genuine bloke and a guy who genuinely bowls fast. the pace he generates is unbelievable.

"My job was to tie down the batsman and his job was to attack."