Tom Collins has been banned for two weeks after being sent off at Wasps on Sunday.
The wing was dismissed in the 65th minute of the match at the Ricoh Arena after an aerial collision with Wasps fly-half Jacob Umaga.
Saints went on to win the match 35-31, despite Collins' red card and a yellow for Cobus Reinach.
But the black, green and gold will now be without Collins for the Champions Cup games against Benetton and Lyon.
He attended a disciplinary hearing at Coventry on Wednesday evening and accepted the charge of tackling the jumper in the air.
Collins will now be free to play again from January 21, meaning he will be able to face London Irish at Franklin's Gardens in the Gallagher Premiership game on January 24.
Independent disciplinary panel chair Matthew Weaver said: “The panel found that the player’s actions were reckless in that he failed in his duty to protect the player in the air.
"They accepted that there was no intent to cause any harm and the player was immediately remorseful for the injury sustained by Jacob Umaga.
"The panel found that this was a low end entry point of four weeks and that the player was allowed the maximum mitigation of 50 per cent due to his acceptance of the charge, his clean record and immediate and genuine remorse."