The citing lodged by the Citing Commissioner for the match, Iain Goodall (Scotland) was for an alleged dangerous tackle on Perpignan player Dan Carter (No 10) in contravention of Law 10.4 (e).
Ellis admitted he was guilty of foul play in that he had committed a dangerous tackle, and as the offence was judged at the top-end of the level of seriousness for a dangerous tackle,will be sideline for period of six weeks up to and including Sunday, 25 January, 2009.
The Ospreys and Tigers are locked at the Top of Pool 3 in the Heineken Cup. Both sides have 15 points after four rounds, and both can still qualify for the quarter-finals as Pool winners, or one of the two best-runner-up spots.
They meet at the Liberty Stadium on Saturday, 24 January, in what could be a Pool decider.