Spinner Ravi Patel will leave Middlesex when his contract expires at the end of the season, after the county said they would not be renewing his deal.
The 27-year-old has spent nine years with the club, taking 139 wickets in all formats of the game.
Managing director of cricket Angus Fraser said: "His first XI appearances have continued to be occasional.
"We believe he has reached a stage in his career where he needs new challenges in a different environment."
Fraser added: "Ravi remains keen to continue to play professional cricket and we wish him well in his search to do this.
"He is an extremely capable bowler and it is a shame that all of us have been unable to consistently get the best out of him."