It is not so much he feels Wenger was wrong to let him leave Highbury, more that when he started to analyse his career, Upson recognised he had not done himself justice.
"Arsenal was a lesson for me," he said. "I left having not touched the potential I had as a young lad.
"I didn't really come through and do the things I knew I could. That was to do with my mental approach.
"It didn't matter how hard I trained, all these other things weren't up to scratch.
"There was a sense of failure and if you behave in the same way then the outcome is generally the same so you have to change your approach."