Saqlain Mushtaq, who signed a two-year deal with Sussex last February, has been released at his request for personal reasons.
Saqlain had not featured much this summer and made only four Championship appearances taking 14 wickets.
"I would like to thank the whole team at Sussex for all the opportunities they have given me this season," he said in a brief statement. "The club has been wonderful and it is with a heavy heart that I am having to say goodbye for my own personal reasons."
As recently as July, Saqlain, 30, who qualifies for England next April under residency rules, was taking about possibly playing for England. But he has been increasingly troubled by knee injuries and this latest news now raises doubts about his future in the game.