But the news isn't so good for fellow defender Garrick Ibbotson, who is unlikely to play due to a lingering problem with his Achilles tendon.
Johnson missed Fremantle's qualifying win over Geelong due to a slight calf niggle.
The Dockers' week off has given Johnson extra time to recover, and he's almost certain to be given the green light to face Sydney.
Rebounding defender Nick Suban is also a strong chance to play the Swans despite rolling his ankle against the Cats.
But Ibbotson, who hasn't played since round 18 and is lacking match fitness, will struggle to force his way back into the side, even if Fremantle reach the grand final.
The Swans will enter Saturday night's match without star forward Kurt Tippett (knee) and promising youngster Tom Mitchell (ankle).
Tippett booted five goals in his team's win over St Kilda four weeks ago, but the key forward has failed to fire in recent games.
Lyon said Tippett's absence probably wouldn't affect the Swans too much.
"Everyone's talking about Tippett, but I think he was only averaging one goal a week over his last three games," Lyon told Perth radio station 6PR.
"I don't think they'll miss him too much.
"Mike Pyke's taken the most contested marks in their forward 50m."
Meanwhile, Fremantle have appointed Simon Eastaugh as their new ruck coach.
Eastaugh, who has been part of West Coast's coaching team since 2009, will link up with the Dockers on November 1.
Fremantle feature a powerful ruck duo in the form of Aaron Sandilands and Zac Clarke, while Jon Griffin, Jack Hannath, Craig Moller and Kepler Bradley are other ruck options on the list.
