Patel, who turns 39 in November, is set to play on, with Derbyshire understood to be favourites for his signature.
Patel made his first-team debut for Notts in 2002, going on to play more than 600 games across formats and collecting six major trophies, including the County Championship twice and the T20 Blast twice. He was also capped 60 times by England between 2008 and 2015.
“It has been a privilege and an honour to represent Nottinghamshire, a place that I have called home for nearly three decades,” Patel said. “The club has played a huge role in developing the young nine-year-old I was when I joined the club into the cricketer I am today.
“I look back on my career at Trent Bridge with tremendous affection; some of my fondest memories have come whilst donning the green and gold in front of the best fans in the world, engaging in battles on the field and winning trophies for the club.
“When I signed my first contract at 15, I dreamt of representing my country in all three formats. I have no doubt that the club’s unwavering support helped me to achieve these goals and, for that, I will be eternally grateful.
“Nothing would have given me greater pleasure than to see out my career with Notts, but whilst I haven’t been offered a new contract at Trent Bridge, I feel determined that I still have a lot to offer the game with both bat and ball. I’m looking forward to beginning my next chapter, contributing on and off the field wherever those opportunities may arise.
“Finally, thank you to all the members, supporters, staff and team-mates who have walked through the gates at Trent Bridge. If it was not for you guys, I would not be the man I am today.”
Source: ESPN Crickinfo