He will miss the Hurricanes' match against the Crusaders in Wellington on Saturday, which was to be his 100th Super rugby match for the franchise.
Cowan sent a letter to Sanzar in support of Nonu, which aided the All Blacks midfield back's case.
Nonu is no stranger to the Sanzar judiciary.
In 2005 he was suspended for a week for a dangerous tackle against the Sharks and copped the same punishment for the same offence three years later. On that occasion he had been yellow-carded for a high tackle on the Highlanders' Clint Newland.
Last March he was cleared of making a reckless tackle on Stormers first five-eighth Peter Grant in the Hurricanes' 37-13 loss at Cape Town.