Spaniard Alex Debon will replace Jorge Lorenzo at the Fortuna Aprilia team in next year's 250cc world championship.
Lorenzo, the current world champion and championship leader, will move to MotoGP next season after signing a deal with the Yamaha factory team.
Thirty-one year-old Debon, a test rider for the team during the past two seasons, will take Lorenzo's seat.
"Dani Amatriain (team manager) offered me a chance that I couldn't reject such as taking Jorge Lorenzo's position in his team," said Debon, who raced at this year's Spanish Grand Prix and who will compete again in next month's race in Brno.
"I'm very excited about the project and I think this is a great opportunity, probably the best of my career. I think I'm ready and I will give it all to pay back for the trust they have put in me."