A 41-year-old test rider will replace nine-times world champion Valentino Rossi while the Italian recovers from a broken leg.
Wataru Yoshikawa will join Jorge Lorenzo in the Fiat Yamaha squad from the Barcelona round of the MotoGP World Championship next weekend.
The two-time Japanese superbike champion will substitute for Italian until he is fully recovered from the broken right leg he suffered in a practice crash at Mugello earlier this month.
It is expected that Yoshikawa will be with the Fiat Yamaha Team for at least three races, after which more should be known about Rossi's expected return date.
Rossi though may not be fit to return until the Brno round in the Czech Republic on August 15 at the earliest.
Yamaha had initially intended for Texan Colin Edwards to move to the factory team as cover for Rossi.
But that created a problem for the Monster Yamaha Tech 3 Team and who could come in and join Ben Spies for at least the Catalunya, Sachsenring and Laguna Seca races.
British rider Cal Crutchlow turned down the chance to move to Tech 3 while continuing his campaign in the World Superbike championship.
As a result, Yamaha opted to draft in Yoshikawa and Lin Jarvis, Managing Director of Yamaha Motor Racing, said: "We have considered many different scenarios and candidate riders to fill the temporary vacant seat in the Fiat Yamaha Team.
"We had always planned to use a rider from within the Yamaha Motor & Tech 3 family but for each rider we considered who is in active competition, their move to the Fiat Yamaha Team would have created another problem for their own racing program or for the teams in which they are engaged.
"Finally, after a great deal of consideration, we have selected Wataru Yoshikawa, our Japanese YZR-M1 Test rider, to join us as our substitute rider. We provisionally plan for three races (Catalunya, Sachsenring and Laguna Seca) but we will adjust the plan accordingly when we know more about Valentino's expected date of return.
"The benefit of Wataru's presence in our team will be threefold. Firstly he brings with him a wealth of experience riding the YZR-M1. Secondly his presence allows us to fulfill our contractual obligations and to join the team's quest to accumulate points for the Team Championship.
"Thirdly he will gain valuable first hand MotoGP race experience in three challenging circuits which w ill surely be very useful to assist him and Yamaha with the future development of the YMR-M1. We look forward to welcoming Wataru into our team while we wait for Valentino's return to full fitness."
Yoshikawa added "I'm happy to have this chance to stand-in for Valentino while he is recovering and to compete in MotoGP again for the first time since 2002, when I raced at Motegi.
"Looking at the Fiat Yamaha Team results with the 2010 YZR-M1, I can see that the winter developments were correct and now I am looking forward to having the chance to gather some ‘real racing' data, which will be very helpful for the future development of the M1."
mcn yes but well see