Sydney coach John Longmire says the prospective season-long absence of versatile 20-year-old Alex Johnson will not subdue his AFL side’s unyielding defence.

Johnson, possessing a rare ability to man both small and tall forwards, played every game in 2012 as the Swans let in an average of just 10.4 goals – the AFL’s stingiest record by some margin.

Johnson is currently deciding whether to undergo a synthetic graft or traditional knee reconstruction after rupturing his anterior cruciate ligament, but would miss half the season even if he does sign up for LARS.

Rebounding premiership defenders Nick Smith (knee) and Marty Mattner (hip) are both yet to play a match this year, with Smith likely to resume on Saturday against Port Adelaide and Mattner also a chance to feature in Sydney’s final pre-season tune-up.

It makes for some difficult defence decisions for Longmire ahead of March 30, when the Swans start their premiership defence with a match against Greater Western Sydney.

“It (Johnson’s injury) will change it (the defence). Because Alex has played almost every game over the past two years,” Longmire said on Tuesday.

“He’s been a really good player for us in our back six. There’s no escaping that.

“But … a couple of years ago an opportunity presented itself to Alex Johnson (when Craig Bolton retired) and he took it with both hands.

“…It’s not unusual. It’s what happens. Players come in and out of the team through form and injury and others grab their chance.”

But they won’t be a like-for-like replacement.

Johnson’s proven himself against a diverse range of players, from Essendon power forward Michael Hurley to Geelong goal-sneak Mathew Stokes.

“(Full-back) Teddy (Richards) can play on smalls and talls. He’s able to play smart and drop off when he needs to and also play on those medium forwards,” Longmire said.

“He’s able to adapt his game and I’m sure others will be able to adapt as well.”

With a slew of stars, including Adam Goodes (knee), having limited pre-seasons, Longmire seems hesitant to pick too many underdone players for round one.

“We’ve still got a couple of weeks to go, so we’ll see what happens,” he said of Mattner and Smith’s chances of taking on GWS.

“…We’re conscious of not playing too many players (in round one) that haven’t had the right amount of preparation.”