Australian Travis McGowan has been released by Somerset Rebels, with James Wright coming in as his replacement.
Stockport's Wright, 25, had been riding with Workington Comets but lost his place during a re-shuffle at the Cumbrian club.
"It is never easy to tell a rider that he is being replaced," said Somerset co-promoter Garry May,
"But Travis just hasn't been able to reproduce the form that we all know he is capable of."
May continued: "No promoter ever wants to release a rider, especially someone like Travis who has been the consummate professional, but for whatever reasons things just haven't worked out for him at Somerset this year.
"James has averaged around eight points a match for Workington this year. I am sure that he will quickly settle into his new surroundings and that we will see a continuation of that sort of form."