The 26-year-old, who claimed World Championship gold at Daegu in 2011, finished in fourth place in a time of 48.24 seconds behind winner Felix Sanchez, who finished in a season’s best 47.63 secs.
And Greene, who refused to take anything away from Sanchez’s efforts, felt his injury-hit build-up to the Games was the difference between failure and success.
“I just felt a bit tired tonight,” said the world and Commonwealth champion.
“The knee injury certainly affected my build-up. I couldn’t start until half way through January instead of October time, but I can’t argue too much.
“I ran a personal best a few weeks ago. I just think that perhaps the endurance wasn’t there for the few rounds and that’s where I missed out on the winter work.
“You can’t always tell if it’s there or not until you get into the majors, and I was bit wanting at the end there. I couldn’t have given it anything else tonight.
“Obviously, everything was a bit shock in the semi-final and everyone went fast. I gave it everything I had tonight, with a bit of a better structure to my race, but I was a bit too tired at the end there and narrowly missed out.”
The Welshman, who was expected to be in a showdown with Javier Coulson, believes the 400m hurdles threw up some fast times and shocks in London, and puts this down to the standard of the competition.
He said: “I know coming in, me and Coulson were way ahead in the rankings,
“But I’ve never been in a race or a competition before where people have gone so far above the expectation until Saturday night, when everybody seemed to surprise me.
“It sort of happened again tonight, with a few of the guys pulling something out. But they’re great competitors and I can’t take anything from them.
“They’ve worked very hard and Felix is a fantastic athlete and worthy winners on the day.”
Michael Tinsley, from the USA, came second with a personal best of 47.91 seconds and Coulson, who was favourite for gold, came third with 48.10, while Sanchez, from the Dominican Republic, won his second gold with the same time he posted in Athens eight years ago.