DEFENDER Alex Johnson is facing a knee reconstruction after suffering a suspected torn anterior cruciate ligament in Saturday's NAB Cup game against Gold Coast in Blacktown.

 

In a hammer blow to the defending premiers, the valuable 21-year-old was taken from the ground on a stretcher just 13 minutes into the game and the Swans fear the worst.

 

"At this stage it looks like it'll be a knee reconstruction," coach John Longmire told reporters after the game.

 

"It'll be confirmed when he gets the scan but (club doctor) Nathan Gibbs is pretty sure that it's a knee reconstruction.

 

"It's terrible news for him and he's an important player for us, but unfortunately it happens a bit in the pre-season.

  

"There's never a good time to do a knee, but when you've been able to do most of the training and on the eve of the season, it's certainly not the best time to do them."

 

Since making his debut in round three, 2011, Johnson has never been dropped due to his form and has played 45 matches over the past two years, including all 25 games en route to last year's flag.

 

The Swans have some depth in the backline, with Lewis Roberts-Thomson slotting into defence in the 36-point win over Gold Coast and Tony Armstrong, Dane Rampe and Harry Cunningham putting their hands up during pre-season.

 

Johnson seemed OK during the second half, seen walking freely with only a compression bandage on his knee, and reporters were stunned by the likely diagnosis.

 

"Sometimes it can actually feel OK afterwards," Longmire said.

 

"I've done a couple and it's not always the best indicator.

 

"We have to confirm it with the scan, but Gibbsy's words were he thinks he's done it.

 

"He's just turned 21 and it wouldn't have him hit yet."

 

James Dampney is a reporter for AFL.com.au. Follow him on Twitter: @AFL_JD