The player will be unavailable for South Africa's fall fixtures.
South Africa front-rower Wessels has been suspended of nine matches for making contact with Josh Murphy's genitals during the Bulls' URC victory over the Irish province.
The incident occurred in the 18th minute of the close contest in Galway on last Friday, with opposing player Josh Murphy being shown a 20-minute red card after reacting angrily by hitting the South African on the head area.
After Murphy complained to the match official, the situation was reviewed by the TMO, who found insufficient clear footage.
Wessels remained on the field until he was substituted in the later stages of the game.
While the United Rugby Championship announced that the Irish player's 20-minute red card was withdrawn by a disciplinary panel, Wessels was found to have breached law 9.27, which specifies:
"A player should not engage in actions that is against the principles of fair play. This includes touching, twisting or compressing the private areas."
The panel concluded that the event met the red card threshold and justified a 12-week suspension, the minimum suspension under World Rugby regulations for such an offence.
However, Wessels' ban was shortened by three weeks because of his cooperative behavior during the proceedings and his clean disciplinary history.
Wessels and the Pretoria-based team have the right to appeal, but as it stands, the ban will rule the 24-year-old out of the Springboks' fall internationals against the Brave Blossoms, Les Bleus, the Azzurri and Ireland.
Wessels will additionally be absent for the his club's URC games against Warriors, the Emirates Lions and the Sharks, as well as European cup fixtures with Bègles and Saints.
Wessels has earned 10 caps for South Africa and was included in their Rugby Championship-winning team over the summer.
The Connacht player, meanwhile, is eligible to play against Munster in Saturday's domestic clash after being cleared.
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