There has been increased focus on concussion since a group of former players launched legal action against rugby authorities, claiming they were not sufficiently protected from and informed about potential brain injuries.
Barclay said he played in the 2017 autumn internationals, unsure whether he had fully recovered from a concussion suffered six weeks before on club duty for Scarlets.
“The autumn Tests were coming up and I thought I felt alright, but I wasn’t sure,” he said.
“I thought I probably was but, looking back, should I have played? Possibly. Probably not.
“But as someone who’s had a history of concussions, Garry Ringrose realises how serious it is. It’s massive, an incredibly selfless decision.”
Ringrose’s withdrawal means the Lions line up with Ireland’s Bundee Aki inside Jones, a midfield combination that has started only once together in the eight matches played by the 2025 Lions.
However, with rain forecast for Melbourne on Saturday, Monye said brute power may be more important that intricate patterns of play.
“Saturday’s not the day for multi-phases and pressure through attack,” he said.
“If it is hammering down with rain, I think that works as an equaliser.
“If you are worried about cohesion and this and that, it’s not going to be that type of game.
“I think it’s going to be probably five or six phases and then get rid of the ball – that type of game.”
Owen Farrell, who was called up to the tour as a replacement for the injured Elliot Daly and played 80 minutes at inside centre against the First Nations and Pasifika XV, is covering midfield on the bench.
The 33-year-old four-time tourist is noted for his distribution and defence, but lacks the gainline power of Aki or Sione Tuipulotu.
“You can try and rank the potential centre partnerships but, with Aki and Jones, we have two really, really good players together,” said Monye.
“My only hesitation is what that centre partnership looks in the final 30 minutes. Is it going to be Aki and Farrell? Is it going to be Farrell and Jones?
“That is going to be a change.”
Barclay said: “The 12s they have picked for this tour – Aki and Sione Tuipulotu – play completely differently to Owen Farrell.
“If you put Farrell in there the game plan has to change slightly.”