Nov 9 (Reuters) - Six-times MotoGP world champion Marc Marquez will miss the season finale at the Valencia Grand Prix this weekend after being ruled unfit following an off-road training accident last week, race organisers said on Tuesday. The Repsol Honda rider has been suffering from vision problems since the training accident in the build up to the Algarve Grand Prix in Portugal, which he was also forced to miss. "During these days of rest, Marc has continued to feel unwell and has suffered from vision problems, which is why this Monday he was visited by Dr. Sanchez Dalmau who examined him and performed the tests, which detected a new episode of diplopia," Repsol Honda said in a statement. The 28-year-old, who has won three races this season, will not feature in post-season testing in Jerez, Spain on Nov. 18 and 19. Yamaha"s Fabio Quartararo sealed the world title following a fourth-placed finish in the Emilia Romagna Grand Prix last month.