"Like many of sports greats, he has gone out on his own terms," Van Hattum told reporters. "His contribution to New Zealand Football has been significant as an inspirational leader in every respect. Without doubt he is one of our all-time greats.
"The fairytale would have been for the All Whites to qualify for the World Cup in Brazil with Ryan at the helm, but this is the reality of professional football.
"These opportunities don't come around too often - it's an exciting chance for him to move into the next phase of his career, and that opportunity is now."
Nelson has been playing in England since 2005.