Saracens will be without captain Brad Barritt for the rest of the month after the centre was banned for three weeks following his tackle on Geoff Parling.
Barritt's team-mate Richard Barrington, who was sent off for his part in the double hit that left Parling unconscious, has been let off the hook after an RFU disciplinary panel rescinded his red card.
The incident occurred early in the first half of Saracens' Premiership clash with Exeter last weekend. Barritt is suspended until 31 January while Barrington is free to play again immediately.
An RFU statement said Barritt's ban was in line with new high-tackle laws.
Barritt had initially tackled Parling high and Barrington followed up with a shoulder into the head of the 33-year-old England international, who was carried off on a stretcher.
Under the new interpretation of the high-tackle rules, which came into effect on 3 January, Barrington was sent off by referee Ian Tempest.
However, the panel at Tuesday's hearing in London judged Parling was already unconscious from Barritt's tackle and fell into the contact with Barrington.
"The incident arose out of the specific dynamic of Mr Parling falling unconscious into what would have otherwise been a legitimate contact by Mr Barrington," the RFU statement said.
"In line with the new sanctions a mid-range entry of six weeks was imposed on Mr Barritt reduced to three weeks in light of mitigation including his guilty plea."
The ban means Barritt will miss Saracen's next two Champions Cup matches against Scarlets and Toulon respectively as well as their Anglo-Welsh Cup game against Scarlets on January 27.