Morgan had been struggling with a knee ligament injury sustained in January 2012, and after a series of setbacks - including an infection which set back his rehab by several months - he has admitted that he simply would not be able to cope with the demands of the modern game.
"The training, playing and continuous process is hard for a fit player, so for me, it just wouldn't be possible," he told the BBC.
Morgan broke into the England team in the 2007 Six Nations, playing against Scotland and Ireland - but he was forced out of the second of those matches with a shoulder injury that ruled him out for the rest of the season.
He was once again called into the national squad two years later for the summer tour but never go the chance to pull on the jersey.
"I was really pleased with how the rehab had gone. But like with many guys who retire with knee injuries they feel they get close, but with professional rugby as it is nowadays, it made me think it couldn't cope," he added.
"The gutting thing is how hard I've worked. That's the hard part to take. You always think in the back of your mind 'can I defy the odds?'. But I know I've made the right decision."