Wessels, 24, was found guilty by a United Rugby Championship disciplinary panel of "grabbing, twisting or squeezing the genitals" of Connacht flanker Josh Murphy when the Bulls edged a narrow win in Galway last Friday.
Murphy punched Wessels during a ruck and told referee Mike Adamson that he was retaliating because his genitals had been grabbed.
There was no conclusive video evidence for the match officials to act on, so Wessels remained on the field while Murphy was red-carded.
However, the citing commissioner reported Wessels for an act of foul play and the disciplinary panel “were satisfied that an act of foul play had occurred and found the incident met the red card threshold, with entry of low-end warranting a 12-week suspension,” a statement on Thursday said.
"The panel reduced the suspension by three weeks (25% mitigation) due to the player’s good conduct prior to and at the hearing and good record, which results in a nine-game suspension," it added.
The suspension starts with Friday’s URC clash at Glasgow Warriors and takes in the Springboks’ Tests against Japan in London on November 1st and subsequent weekend internationals in France, Italy and Ireland.
Wessels, who has won nine caps for South Africa and was part of their squad that won this year’s Rugby Championship, will also miss four more games for the Bulls in December - two in the URC and two in the European Champions Cup.
The sanction can be appealed, but the Bulls have yet to make a statement on whether they intend to do so.