Mikhail Botvinnik in 1933. Image credit: wikimedia.
Found here is the first (to the best of my knowledge) mention of Botvinnik in the Jewish press, Davar, 3.12.1931:
A 20-Years-Old Young Jew -- USSR Chess Champion.As can be seen by the (over) emphasis on the players' Judaism -- the word 'Jew' or 'Jewish' is mentioned four times, once redundantly, in a three-sentence article -- the Jewish press in Palestine at the time was rather overly patriotic...
In the large tournament in Moscow that ended in November, the young Jew Mikhail Botvinnik (Jewish) (sic). 80 of the best players in the USSR took part. Botvinnik, which won 13.5 out of 17 points, was crowned 'USSR Chess Champion' and won a large cash prize. Second was Riumin and third Verlinsky (Jewish).