The 34-year-old has retired from football after making more than 240 appearances for the Saints.
He then played two seasons at Leicester City until 2023, and has not played for a club since then.
The former Chelsea defender stated on Sky Sports: “Just to clarify officially, I will be retiring from football.
"It's been a little while but I get asked a lot of questions, like ‘When are you coming back, what are you doing?'
"So, just to make that official, I am retiring and very much looking forward to the next steps.
"From dreaming as a young boy to going on to achieve what I have achieved is absolutely unbelievable.
"I am forever grateful when I look back. I have always been ahead of the curve and I'm super excited about the business of the game.
"I felt I had things in position to transition quite easily. I very much look forward to that. I decided to start the next journey.
"I was fortunate enough to study the game and understand what I wanted to do next and what my purpose would be.
"I'm getting the wheels in motion for that now. I'm obsessed with the business of sport.
"I very much see myself (asking) 'How do I contribute to the evolution of football?' It's an exciting future ahead.”