Lyon (back), Tate (shoulder) and Gidley (shoulder) are all listed as doubtful starters for the end-of-season tour of France and England while selectors are already without Roosters centre Justin Hodges (knee).
Tate, who missed Brisbane's season-ending loss to Penrith on Sunday, has a nerve problem in his shoulder while Gidley, who also broke a rib in Saturday night's loss to the Sydney Roosters, will see a specialist this week.
"I'll just see how it goes," Tate said.
"I feel pretty confident I will be right. I want to go on tour.
There's a lot of hard work on tour but there's a lot of good fun as well.
"You'd die to go on a Kangaroo tour."
Girdler, who will turn 31 on Friday, has played five tests for Australia, but made his last appearance two years ago against New Zealand.
But he looms as a realistic option for selectors following an outstanding end of the season.
Girdler produced a starring role for Penrith to help the Panthers turn a 14-point deficit into a 28-18 win over Brisbane in the fourth National Rugby League qualifying final against Brisbane at Penrith Football Stadium.
He put the Panthers in front for the first time with a second-half intercept try and also landed four goals from five attempts for a 12-point contribution.
"He hasn't been getting the recognition he deserves," said Penrith captain Craig Gower.
"He's definitely come back into form. He's one of the top-class players in the club and in the competition."
Penrith coach John Lang described Girdler as a genuine big-match player.
"It seems the bigger the game, the better Ryan plays," Lang said.
"Ryan has played at the very top level. He's got pointscoring records in State of Origin, he's played at the elite level a lot, he's excelled at the elite level.
"I've always believed that Girds seems to kick the big goals.
He's got a great skill and that's what you expect from your big players."
Lyon (back) is also unlikely to tour despite being named in the train-on squad, while Gidley and Tate are expected to be added to it on Monday following Brisbane and Newcastle's elimination from the finals series.
Newcastle lock Ben Kennedy (foot) and winger Timana Tahu (knee and shoulder), who has missed most of the past month, are also under a fitness clouds.
However, national selectors are expected to name a handful of Newcastle players in the train-on squad.
Kennedy, Gidley and Tahu will be selected alongside hooker Danny Buderus and prop Josh Perry.
Back rowers Steve Simpson, who played test football last year but missed the representative season in 2003 through injury, and outstanding youngster Daniel Abraham should also come under consideration.
As should former test winger Adam MacDougall, who scored 11 tries in 12 games after returning from a long-term knee injury in June.
The Kangaroos stocks have already been depleted with St George Illawarra prop Luke Bailey (ear) ruling himself out of the tour on Friday.
His teammate Shaun Timmins is also in doubt due to ongoing knee problems while the likes of Andrew Johns (neck), Trent Barrett (leg) and Jason Ryles (shoulder) have already been ruled out of the tour