Green, currently enjoying no 1 status because of the injured Cesar, moved to Loftus Road in July having helped West Ham win promotion back to the Premier League.
But after opting to test himself with another top-flight club in London, Green had to contend with a miserable spell on the bench following the arrival of Cesar from Inter Milan at the start of the season.
"I came to QPR looking for a new challenge after six years at West Ham, a wonderful time capped off by promotion at Wembley," Green said.
"Kevin Hitchcock, the goalkeeping coach at QPR, is an old mate and I came to work for him on the understanding that I was first choice.
"If he'd said to me we're also going to sign someone who's won Serie A five times and the Champions League and is one of the biggest names in South American football, I would have thought twice before signing.
"I'd read rumours in the press about Julio coming, but when I asked officials at the club they dismissed it as paper talk and said he wasn't going to sign."
With Green also pushing hard for the England jersey, his demotion was even harder to take.
"Now that the Brazilian had joined the club I needed to know where I stood," Green added.
"I asked Mark Hughes. He told me Julio was going to play, that I'd done nothing wrong and that he wanted two top keepers competing for the position.
"I replied, 'Well, if he's going straight into the first team he's not really competing, is he? Where does that leave me? Hughes replied, 'You're free to leave whenever you want'. It wasn't quite what I wanted to hear."
On the back of Harry Redknapp stepping into the shoes of sacked Hughes last month and the injury to Cesar, Green is now determined to make his mark.
"I'm in the jersey now and it's up to me to play well enough to keep it," he said.
"I believe Harry when he says it's a fair fight on form alone so we'll see how it all turns out."