John III Potho of Pothenstein (also spelled Pottenstein; died 1390) was Bishop of Bishopric of Münster from 1379 to 1382.
Potho was a member of a Czech-speaking Bohemian noble family based at Pottenstein Castle (now Potštejn in the Czech Republic).
En route to Münster, Potho and his entourage were attacked near Hamm by the Count of the Marck.
Immediately after Potho's arrival in Münster, he created several indulgences, with papal permission.
He did not understand the Low German dialect spoken in Münster and this made relations with his subjects problematic.
However, the cathedral chapter refused to recognize him and elected John IV Junge instead.
[1] Even after John IV's death, Potho was unable to take up de facto government.