Western Bulldogs captain Brad Johnson says neither his poor performance against Collingwood nor the team's need for an emotional spur prompted Monday's retirement announcement.

Johnson's decision to leave the sport at season's end means Saturday night's do-or-die MCG semi-final against Sydney will be the curtain call for one of the league's most-loved figures.

Either the 362-game veteran - guaranteed selection despite struggles with a nagging Achilles injury and form queries - or Sydney stalwart Brett Kirk, who has previously announced his retirement, will bow out.

The 34-year-old Bulldogs games record-holder said he decided midway through the season this would be his last, initially telling wife Donna, before broaching the subject with coach Rodney Eade.

Eade encouraged him to wait until the end of the season before finalising the decision, posing the idea he could relinquish the captaincy but play on.

But with the Achilles injury having kept him to 13 games so far this season, and the likelihood of several post-season operations, Johnson had to acknowledge what his body was telling him.

He said his lack of influence in Saturday night's 62-point thumping from the Magpies, which prompted many commentators to question whether he warranted continued selection, was not the catalyst.

"No, not really, I'd made my decision, probably like I said, you know quite a while ago that this would be it," Johnson said.

"So no, not at all. Yeah I played poorly on Saturday night, it was more my skill level that dropped off on Saturday night.

"My last month of footy has been up and down. I didn't play that well against the Cats and then played a quarter-and-a-half against the Swans and missed another week.

"So hopefully with that run under my belt (against Collingwood) I can certainly bounce back and lead the guys, which I really enjoy doing, into an elimination final."

The announcement will counter the emotional effect of the inspirational Kirk's imminent retirement on the Swans.

The Bulldogs desperately need a spark, having been hit by injuries and tailed off badly in form, with three losses in their past four games.

As well as Saturday night's thumping by the Magpies, those defeats included a 101-point belting by Geelong and a 44-point loss to the Swans.

But, while Johnson still harboured the dream of going out with a premiership, he said his teammates did not need the added incentive of trying to deliver one for him.

"I certainly didn't want to use it as that sort of motivation," he said.

"At the end of the day, I get the opportunity to pull the jumper on, hopefully three more times, but it's not so much for the playing group.

"We know what we've got to achieve and going into a final ... one thing we certainly don't believe in is that false motivation.

"We've got our own motivation, we've got our own belief that we'll certainly stick by."

Johnson, who made his debut at Whitten Oval against Collingwood in 1994, five days after his 18th birthday, said it had been a "dream come true" to play out his career with his local club.

A six-time All Australian and three-time best and fairest, he said even if he failed to finish with a flag, he would leave the game proud he had given everything he could.

Eade ranked Johnson near the top of the list of players he had played with or coached, as well as being a great leader.

"People outside the club have underestimated how important his leadership has been to this club," Eade said.

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