England lock Courtney Lawes has been banned for two matches for "recklessly striking" Argentina's Mario Ledesma with his knee on Saturday.
The 22-year-old will miss England's next two games, against Georgia on Sunday and Romania on 24 September.
Lawes, who pleaded not guilty, will be available for England's final group game against Scotland on 1 October.
Judicial officer Terry Willis said he applied some leniency because of Lawes' disciplinary record and "remorse".
The offence carries a guideline suspension of between three and 12 weeks - converted to matches at a World Cup - but Lawes' offence was deemed "low end".
England have 48 hours after the decision in which to appeal, and have not yet revealed whether they intend to do so or not.
Lawes was found guilty of striking Ledesma with his knee during the first half of England's World Cup opener against the Pumas, which they won 13-9. Lawes was cited for an infringement of law 10.4(a), which concerns "punching or striking (with the knee)".
The Northampton forward had charged across to try and stop Ledesma crossing in the right corner. The veteran Argentine hooker took a knee to the head and lay motionless for several seconds.
England manager Martin Johnson said: "It is a fast-moving game and he dived to make what he thinks is a try-saving tackle. We thought any contact was incidental but they thought differently."
A statement from Rugby World Cup Limited read: "Having conducted a detailed review of all the evidence available, including all broadcast angles and additional evidence from the player and submissions from his counsel, the judicial officer upheld the citing on the basis that the player had committed an act of foul play.
"However, taking into account mitigating factors being his excellent disciplinary record and remorse and the absence of aggravating factors, the player was suspended for two weeks."
Lawes, who has 11 international caps, was also involved in a controversial tackle on Gonzalo Tiesi, which caused the centre to be ruled out of the tournament with knee ligament damage.
However, Lawes was not cited for this incident.