Parramatta has recruited former NRL salary cap auditor Ian Schubert to help it find a way to squeeze under the 2016 cap before their clash with South Sydney next Friday.
Johns said the Eels could be forced to offer players to rival clubs at bargain prices, making the club helpless to avoid paying a significant amount of players' wages even after they have moved to a rival team.
He said rival clubs have their own salary cap restraints for 2016 and will attempt to force the Eels to pay more than half of the wages for any player that is forced out of Parramatta.
It means the Eels must lose at least one star player earning big money or be forced to dump up to a quarter of its top 25 players.
"They have to shed some players on the salary cap and it's tricky," Johns told Triple M's Grill Team.
"It's not straight forward. Firstly, they need to convince Anthony Watmough to retire.
"(But) it's not just about Watmough. They are going to have to get another couple of players to go."
He said rival clubs are not interested in recruiting the Eels' off-cuts earning close to the NRL's minimum wage of $85,000 for full time players.
"Other clubs at the moment don't want $100,000 players," he said.
"They want Corey Norman. They'd like Semi Radradra. Parramatta don't want to let those players go and nor should they. This is where it gets a little bit difficult and this is where sometimes politically clubs lean on other clubs and get a favour or two."
Panthers legend Mark Geyer said Eels rake Nathan Peats and forward Kenny Edwards would be at the top of rival clubs' shopping lists alongside Norman and Radradra.
"Out of the established players they have, the two that have stood out for me this year are Nathan Peats - he'd be great at any club - and Kenny Edwards," Geyer told Triple M.
"Kenny Edwards can play back row, front row, five-eighth. He's the bloke I'd love at my club."
Radradra and Watmough are the two players most likely to be forced out, Fox Sports' James Hooper reported.
"The retirement of Anthony Watmough is being fast-tracked behind the scenes," Hooper reported.
"If he can leave the club effective immediately then that will most definitely free up some salary cap space.
"The other name I'm hearing, but I have not had it confirmed, is Semi Radradra.
"Semi remains upset at the fact that he's owed some third-party money by the club that hasn't been forthcoming. I have heard that he could potentially become another player that the Eels (can move on) with the club needing a quick fix."
Losing just those two players is unlikely to be enough for the club to be salary cap compliant this season.
If Watmough's retirement is approved by the NRL and the club is allowed to pay out his contract outside the salary cap, only around $400,000 would be written off the club's 2016 cap.
The 32-year-old is reportedly earning around $800,000 at Parramatta, including third party sponsorships, but he has already been paid half those wages this season, meaning just $400,000 would come off the books.
The Eels would also have to promote a player to its senior list earning at least $42,500 - the minimum they are allowed to pay a player for half a season under the NRL's collective bargaining agreement.
Every player released must be replaced by a player promoted from the club's second-tier cap, adding at least $42,500 back onto the 2016 books.
Combined with the likelihood of the Eels being forced to pay a significant percentage of the wages for any player that transfers to a rival club, it seems unlikely the Eels will be able to get away with cutting just a few players.
Grant Mayer, the former Wests Tigers and Manly chief executive and current boss of newly crowned A-League champions Adelaide United, said he would be "staggered" if the Eels could get cap compliant in nine days.
"It's almost impossible," Mayer said.
"You have got to have the desire of the club and the players would have to want to move and that's the challenge.
"Players who have got contracts expect that they won't be any worse off if they relocate," Mayer said.
"That's the issue, there's six months of the season gone and they'd want at least 50 per cent of any figure, plus they might have two or three years left.
"Plus the relationships that will be lost.
"The player should be no worse off. It's a complex negotiation and I'd be personally staggered if they can get it sorted before (taking on the Rabbitohs)."
