Teimana Harrison will miss Saints' trip to Newcastle Falcons after being handed a one-week ban for being sent off at Bath last Friday.
The No.8 was dismissed by referee Adam Jones in the 67th minute of the defeat after dipping his head towards the face of Bath prop Nathan Catt.
Josh Lewis kicked the resulting penalty, handing Bath a 13-12 victory and a place in this Sunday's Anglo-Welsh Cup final at Kingsholm.
Harrison was called to attend an RFU disciplinary hearing in Coventry on Tuesday evening and accepted the charge of striking with the head.
The low-end entry point for that offence is four weeks, but Harrison's previous good behaviour saw that reduced by half and the panel decided that was still too harsh, reducing it by a further week.
He was given a suspension of one week, meaning he misses the Newcastle game and is free to play again on March 27.
Chair of the panel Gareth Graham said: "Teimana Harrison accepted the charge that he struck Nathan Catt with his head.
"The panel heard evidence that contact was minimal and that no injury was caused.
"Unlike other offences involving a strike to the head, there is no mandatory entry point for a strike with the head to the head of an opponent.
"Having had the benefit of hearing from the player and from Mr Catt, the panel had no hesitation in finding that the action merited a low-end entry point, which carries with it a four-week sanction.
"The panel was impressed by the player’s record, both on and off the field, and his remorse was obvious; he clearly satisfied the requirements to receive the full 50 per cent reduction by way of mitigation.
"On balance, the panel determined that such a sanction was wholly disproportionate to the level of offending and that a one-week ban was appropriate."
The disciplinary panel comprised Graham, with Tony Wheat and Ruth Middleton.