Dovizioso will leave Ducati at the end of the season, bringing an end to his eight-year association with the team and said last month that becoming a test rider was "a big option".
But La Gazzetta dello Sport reported that Dovizioso's manager Simone Battistella had communicated the rider's decision to Yamaha Motor Racing managing director Lin Jarvis on Saturday, adding that the 34-year-old would not ride in 2021.
Yamaha were not immediately available for comment.
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Dovizioso has won 13 races since joining Ducati in 2013, finishing runner-up in the championship in the last three seasons. (Reporting by Julien Pretot; Editing by Ken Ferris)
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