Sydney defender Alex Johnson will make a remarkable return to senior footy against Collingwood at the SCG on Saturday night.

Johnson, who last played for the Swans in the 2012 Grand Final win over Hawthorn, has undergone five knee reconstructions and countless other knee surgeries to counter a serious infection in the joint, since he first ruptured his ACL in the lead-up to the 2013 season.

When he runs out against the Magpies it will be 2136 days since the popular clubman was one of the team's best in the Swans' gripping flag victory over the Hawks, his 45th senior appearance from a possible 49 matches.

To put Johnson's journey into context, Heath Grundy has added 140 games to his career tally since that Grand Final, while All Australian defender Dane Rampe wasn't even at the club.

Sydney coach John Longmire told Johnson he'd been picked to face the Pies on Wednesday morning, and the defender said it was the anticipation of that moment that kept him going over the past six years.

"I've been through a lot, but I always had my sights firmly set on getting back into the AFL," he said.

"Ask anyone who is close to me and they'll tell you I wouldn't have given up until that happened.

"There were times when I was lying in a hospital bed that I questioned if it would ever happen, so I'm over the moon."

The 26-year-old's hopes of a fairytale comeback looked dashed when he was delisted at the end of last season, but Sydney re-drafted him to the rookie list and, despite undergoing groin surgery early in the season, he's shown some solid recent form in the NEAFL.

Johnson has played the past seven reserves games and while Sydney had the bye last week, he gathered 22 possessions against Gold Coast at the SCG on July 21 and said his body has felt great in recent weeks.

"I had a few challenges pre-season with my groins but now I feel like I'm moving as well as I ever have," he said.

"I'm really confident in my body going forward and that has given me the ability to play at the level I needed to be at to get back into the AFL."

Longmire said the Swans' coaching staff had been closely monitoring Johnson's form in the NEAFL over the past two months, and he was more than ready to have an impact at AFL level.

He also stressed that Johnson's selection was warranted and had nothing to do with any emotional lift it might give the Swans on Saturday night.

"He absolutely deserves a game, we don't give them away," he said.

"it's not a shock or a surprise, he's been playing really well in our reserves for quite a while now."

Johnson was in his second season when he starred in the 2012 premiership as a 20-year-old and looked set to develop into one of the game's best rebounding defenders.

But while his long list of setbacks threatened to wreck his career, the Victorian never abandoned his dream.

The story has inspired the footy world, especially those at the Swans including his teammates past and present, but Longmire said the backman's footballing talent had often been forgotten amid his comeback story.

"When he first hurt his knee, we were looking at Alex as being the full-back or centre half-back at this football club for the next 15 years," he said.

"The expectations on Alex to be one of the defensive generals for this football team were absolutely there.

"Then he went through his first, second, third and more operations, but that’s still in your mind, and you're hoping you can get to a point where you can play him, because he was a very, very good player."

Longmire joked that Johnson's magnet hasn't changed since he removed it from the whiteboard at the SCG at the end of the 2012 season.

"I had to dust it off, it's fair to say it had an inch or so of dust on it," he said with a laugh.