The 21-year-old was found guilty of a dangerous tackle during Friday night's defeat to Edinburgh at the Parc y Scarlets.
Turnbull was yellow carded for the offence on Edinburgh centre Nick de Luca on the night and has subsequently been banned from all competitions until January 14.
The suspension rules Turnbull out of the Magners League derby clashes with the Ospreys and the Dragons on Boxing Day and New Year's Eve respectively, as well as the Scarlets' first game of 2010 - the trip to Munster on January 10.
Turnbull will also be unavailable for the European double header against reigning Heineken Cup Champions Leinster this weekend and next.
And with a break for European fixtures and then the Six Nations seeing Magners League games put on hold following the Scarlets' encounter at Munster, Turnbull will not be back in Magners League action until February 20.
Guinness PRO12
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