Turnbull saw red in the second half of the game in Parma after referee George Clancy deemed the player to have committed an act of foul play against Maxime Mbanda.
Following the incident the PRO14 confirmed Turnbull’s ban in a statement on Thursday.
It read: “The player was shown a red card by the referee under Law 9.13– A Player must not tackle an opponent early, late, or dangerously. Dangerous tackling includes, but is not limited to, tackling, or attempting to tackle an opponent above the line of the shoulders even if the tackle stars below the line of the shoulders.
“The Judicial Process was handled by Tommy Dalton (Ireland), who concluded that the act warranted a mid-range offence, and that the actions of the player were not deliberate but reckless.
“The Player’s acknowledgement of the offence, compliance throughout the process and remorse shown justified mitigation of 50 per cent, meaning the Player is banned for a period of three weeks.
“The Player is free to play from midnight on Tuesday, November 3.”