ALEX Johnson's fairytale return to AFL football could be over after just two games after the Sydney defender suffered a suspected serious knee injury late in the first term of the Swans' clash against Melbourne at the MCG on Sunday.

Johnson's "good" right knee appeared to buckle when he went to change direction as he chased Demons spearhead Jesse Hogan near the boundary line.

SWANS PIP DEES Full match coverage and stats

The Swan was assisted from the ground by two trainers and did not appear to be able to put weight on his leg.

Sydney football manager Tom Harley told Channel Seven at the first break the club suspected Johnson had suffered yet another ruptured anterior cruciate ligament

"It's the knee he hasn't had any trouble with at this stage. It looks like an ACL (injury) which is disappointing obviously for everyone," Harley said.

"He's certainly a much-admired character so it's disappointing for him."

Nic Newman in tears with Alex Johnson post-match. Picture: Michael Willson, AFL Photos

Swans coach John Longmire said Johnson's injury meant there were mixed emotions in the rooms after his team's brave nine-point win.

"It's a strange feeling for everyone to be honest. You have just had a great win and you really reach down into the depths of your character for that win and we were thrilled with it and you come off the ground and Alex has got a suspected ACL on his good side so everyone digesting that, including Alex," Longmire said.

Melbourne coach Simon Goodwin's thoughts were also with Johnson after the match.

"We all play this game and love this game for a reason and it's been a great story for him to get back out there and it was really sad to see him go down today," Goodwin said.

"As a footy club, I'd like to pass on regards to Alex and his family and hopefully we see him back again."

The Swans lost another defender with Nick Smith not returning after the quarter-time break with an upper leg injury.

"I don't know whether it's a high hamstring or glute (injury)," Longmire said in his post-match press conference.

Just last round, Johnson returned from five knee constructions in his left knee to play his first senior game since the 2012 Grand Final, performing an important role in defence in the Swans' thrilling two-point win over Collingwood.

All of the Swans' players went to console Johnson as he limped into the team huddle at the quarter-time break.

Johnson has managed just 47 AFL games since being picked by the Swans with pick No.57 in the 2010 NAB AFL Draft.

He was delisted in 2017 but the Swans then used their final selection in the rookie draft to keep him on their books.