The Samoan was cited under both law 10.4 (e) for an alleged dangerous tackle and law 10.4 (a) for allegedly punching or striking in the same incident with D'Arcy.
The incident took place in the 19th minute of Munster's 13-9 win in front of a Magners League record crowd.
Mafi's disciplinary hearing took place at the Irish Rugby Football Union's Ulster Branch offices in Ravenhill earlier today.
Mafi was found guilty under law 10.4 (e) for a dangerous tackle and the panel of chairman Hugh Logan, Stephen Hilditch and Ian McIlrath decided that it was at the top end of entry for such an offence.
The panel took into account the player's previous good disciplinary record before they banned him up to and including Sunday, November 21.
The ban rules Mafi out of Munster's opening two Heineken Cup games against London Irish and Toulon, as well as their next three Magners League fixtures against Benetton Treviso, Ulster and the Scarlets.
Mafi will next be available for selection in the Magners League clash with the Dragons at Rodney Parade on Friday, November 26, although he is free to appeal the decision.
63x46.png){kind=logo}