Mathieu Bastareaud has been suspended for three weeks after the Toulon centre made a homophobic slur during a Champions Cup match against Benetton.
Bastareaud had been cited for verbally abusing Benetton's Sebastian Negri Da Oleggio, following an independent disciplinary hearing in London on Tuesday.
The Frenchman was given a six-week ban but it was reduced to three as there were no aggravating factors and because he pleaded guilty.
It comes just hours after Bastareaud had been included in France's Six Nations squad, but he will now miss the opening match against Ireland on February 3.
Tempers flared in the final minute of last Sunday's game at Stade Felix Mayol after Toulon centre Bastareaud conceded a penalty for a swinging arm on Sebastian Negri.
Negri took exception to the challenge and shoved Bastareaud, with the Benetton flanker's team-mates and referee Luke Pearce quickly stepping in to separate the players.
Television footage then showed Bastareaud making the comment, which he apologised for on Twitter on Sunday.
"Good evening everybody, I want to apologise to my response to the insults of the Italian player," he said.
"I reacted badly in responding to his provocation, I am sincerely sorry for the people I hurt."
Toulon ran out 36-0 winners over Benetton to move top of Pool 5. Bastareaud will miss the crucial winner-takes-all clash against second-place Scarlets on Saturday, live on Sky Sports Action.
Bastareaud will be free to return on February 24 for the Top 14 match at La Rochelle.
He has the right to appeal the decision.