Ntamack picked up a yellow card for a shoulder-to-head tackle on Ben Thomas late in France's 43-0 drubbing of Wales in their opening Six Nations fixture on Friday, which was upgraded to a red card following a review.
The disciplinary committee determined that the mid-range entry point of six weeks/matches was appropriate but reduced this to three after the player accepted he committed an act of foul play, along with Ntamack's exemplary disciplinary record.
The player was also given permission to apply to take part in World Rugby's Coaching Intervention Programme to substitute the final match of his sanction.
The Six Nations confirmed Ntamack would miss Saturday's match at Twickenham and said details of when he can return to action would be confirmed in due course.
France face Italy in Rome on February 23rd, before matches against Ireland and Scotland.