Ulster lock Dan Tuohy has avoided a citing for the elbow blow that hospitalised England fly-half Toby Flood.
Flood, the Leicester captain, was knocked out during last Saturday's pre-season victory for the home side at Welford Road and spent the night at Leicester Royal Infirmary where scans revealed no further damage.
However, the 28-year-old will miss the Tigers' Aviva Premiership opener against Worcester at Welford Road on Sunday on medical advice.
Tuohy was sin-binned for the offence but the Rugby Football Union have revealed they would be unable to take any further action due to a disciplinary loophole - that they will see now seek to close - arising out of the game's pre-season status.
"Ulster players were not subject to the RFU's jurisdiction in this match and as a result no action can be taken," an RFU spokesperson said.
"Clubs can agree how discipline should be dealt with in advance of such games and we're looking to see how we can make sure this always happens in the future."
The inability to cite Tuohy will further infuriate Leicester director of rugby Richard Cockerill, who earlier this week called for the incident to be investigated.
"It's these sort of things that will stop little Johnny coming to mini-rugby on a Sunday morning," Cockerill said.
"Once again, our playmaker has been hit and we have lost him from the game. It is illegal. You would expect the powers-that-be to have a look at that."