The 32-year-old England stopper made the switch from West Ham in July having helped the Hammers win promotion back to the Barclays Premier League. However, QPR's decision to sign Brazilian Cesar from Inter Milan a month later came as a huge shock to Green, who soon found himself playing a bit part under manager Mark Hughes.
"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 told the Mail on Sunday. "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."
Green added: "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."
Green admitted the three months that followed Cesar's arrival were among the hardest of his career.
"Now that the Brazilian had joined the club I needed to know where I stood," he said. "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."
Hughes' dismissal last month, and an injury to Cesar, have finally allowed Green a chance to show what he can do between the posts. And the goalkeeper is hoping he can make an impression on new boss Harry Redknapp.
"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."