The Warriors centre will miss both legs of the 1872 Cup derby with Edinburgh.
McDowall was cited after a complaint was made by match citing commissioner Deker Govender, who alleged contact with the eye or eye area of Toulon's Argentina back-row, that should have led to a red card.
When he appeared in front of the disciplinary committee on Thursday morning, McDowall accepted he had made reckless contact with the eye.
The panel, comprising Antony Davies (England, chair), Ken Owens (Wales), and Stefan Terblanche (South Africa) decided the offending was at the low-end of the scale of seriousness, imposing an entry point of six weeks' suspension.
McDowall then received a three-week reduction due to his good disciplinary record and timely acceptance of the charge.
McDowall will be free to play from January 13.