Vickery, who has spent 11 distinguished years at Kingsholm and made 104 appearances in all competitions during that time as well as winning 47 England caps and the World Cup in 2003, has decided he needs time to evaluate his future opportunities.
He is currently involved in a rehabilitation course following a back operation in January - the third of his career - and has shown great levels of commitment and courage in attempting to regain match fitness.
Head coach Dean Ryan said: "I am disappointed to lose a player of Phil's distinction, leadership qualities and undoubted skill. He has been a talisman for Gloucester Rugby for 10 years and his experience was fundamental in our progress.
"He has attained the highest levels possible in the game - has captained his country and won the World Cup - and reluctantly we have to accept his decision.
"The key thing now is to ensure the continued support and development of our young but exceptionally gifted squad for the long-term."
Phil Vickery said: "The hardest decision of my life was to leave home at 19 and without a career in front of me. I was lucky enough to find that Gloucester became my home and the decision to leave the club now after 11 years is the second hardest of my life.
"Gloucester is a place that eats, breaths and sleeps rugby and when you are a player in that environment it inspires you. I have given everything I possibly can for the club, I am proud of my contribution to Gloucester's history, and believe their band of young players is highly exciting for the future.
"Several of my close friends, who I have grown up with and played with throughout my career have moved on and that also had an impact on my decision.
"I want to be happy and I want my family to be happy. Money has never been an issue for me in playing the game I love - the motivation to play has to come from within - but to maintain that level of hunger it is time to assess my options.
"Gloucester Rugby has, and always will, remain a very special part of my life and career."