Ulster number eight Nick Williams is facing a lengthy ban after being cited for allegedly striking Rhys Patchell in his side's 36-17 win over the Cardiff Blues on Fright night.
The New Zealander was shown a yellow card for the first half incident for which Patchell required 10 minutes of treatment before being stretchered off.
Williams' forearm appeared to connect with the out-half's head but Italian referee Marius Mitrea ruled that Williams had gone in carelessly and deemed the offence only worth of a sin-binning.
Patchell spent the night in hospital in Belfast in line with concussion protocols but has since returned home to Wales.
Cardiff coach Dale McIntosh fumed afterwards and was adamant that Williams should have been shown a straight red card.
"A forearm to the head? It should be a red card. I've done it enough, I should know," he said.
Williams has been cited under Law 10.4 (a) - punching/striking, which states that a player must not strike an opponent with the fist or arm, including the elbow, shoulder, head or knee.
A decision is expected later this week but it looks certain that he will serve a lengthy suspension.