Fremantle have taken all 25 players in their squad to Melbourne ahead of Sunday's crucial match against North Melbourne.
Captain Matthew Pavlich has yet to train this week as he battles leg soreness and has to prove his fitness in a light training session before declaring himself fit and available for the coaches.
All emergencies - Zac Clarke, Dylan Roberton and Cameron Sutcliffe - travelled with the team in a sign there may be some changes before bouncedown on Sunday.
Pavlich kicked three goals against Richmond at the weekend but came off the field on a number of occasions for treatment on his hamstring, groin and calf.
Ryan Crowley (ankle), Nat Fyfe (ankle) and Tendai Mzungu (shoulder) have also been under injury clouds over the past week.
Lyon said Pavlich was struggling with “soreness, injuries, corked hammy - all those things”.
“It’s a 50-50 at this point,” Lyon said.
“We’ve planned an alternative ... but I think he’ll get up.
“We won’t take anyone that can’t perform in. Once you nominate yourself, you’re fully fit, so that’s the way it works.”
When asked what Pavlich had to do to prove his fitness, Lyon replied: “Walk in and say, 'Coach I’m happy to play'.
“We’ll give him some physical stuff. He did some work today, he just didn’t do any full training.”
Should Fremantle (12-8) lose to North Melbourne, Carlton (11-9) would be in the box seat to snare a top-eight berth ahead of the Dockers due to their superior percentage.
The Kangaroos (13-7) have won nine of their past 10 matches to surge into sixth spot, with Lyon rating North Melbourne as the form team of the competition.
“They’re not unlike Carlton in 1999 - struggled in the first half and then just flew home ... and made it to a grand final,“ Lyon said.