The right winger went charging into opposite number Andre Osborne while the Irishman was fielding a high ball, resulting in the Leinster player landing awkwardly. Osborne escaped without injury, but on-field referee Ben Whitehouse showed de Klerk a straight red card. The Bulls managed to eke out a 21-20 win over the Irish giants with 14 men.
However, de Klerk's good disciplinary record counted in his favour for the decision.
"During his disciplinary hearing led by John Kirk, De Klerk was found guilty of foul play for his 74th-minute mistake under Law 9.17, which states, 'A player must not tackle, charge, pull, push or grasp an opponent whose feet are off the ground'," read a statement from the United Rugby Championship on Thursday.
"Kirk found that the incident met the red card threshold, with a low-end entry point, which warrants a four-week ban. At the hearing, Sebastian accepted that he committed an act of foul play, which warranted a red card.
"Based on mitigation, he was subsequently given a two-week/game suspension due to his immediate apology on the field and throughout. His good record and exemplary conduct throughout the disciplinary process also helped him receive a 50% suspension of his sanction."
As such, de Klerk is set to miss out on Saturday's clash against Zebre at Loftus Versfeld, as well as next weekend's Challenge Cup last-16 encounter against Bayonne in France.