Cardiff Blues coach Dale McIntosh says Ulster's Nick Williams should have been sent off for the incident that led to Rhys Patchell being taken to hospital during their Pro12 loss in Belfast.
Williams was sin-binned after his forearm appeared to connect with Patchell's head.
McIntosh told Scrum V: "A forearm to the head? It should be a red card. I've done it enough, I should know."
Ex-Ireland centre Maurice Field said: "It was not a forearm smash,".
However, Field told BBC Northern Ireland that number eight Williams had executed "a reckless challenge".
Field added: "Patchell is unfortunate - full-backs do not usually find themselves in those ruck situations.
"Nick Williams is a physical guy, that is the nature of his game."
Scrum V pundits Phil Davies and Mark Jones, two former Wales internationals, agreed with McIntosh's assessment that Williams deserved to be sent off at Kingspan Stadium.
Patchell needed treatment for almost 10 minutes before being taken from the pitch on a motorised stretcher and was to spend the night in hospital as a precaution amid concussion fears.
Blues team manager Gafyn Cooper said: "Hopefully he's okay. The medics have to go through the right protocol."
Blues centre Cory Allen and Ulster midfielder Stuart Olding also departed earlier in separate incidents that did not appear to involve any foul play.