The British and Irish Lions forward was sin-binned during the 11-9 loss to Wales in Cardiff, guilty of a foot-led lunge on Dwayne Peel, his boot making contact with the scrum-half's head at a ruck.
Although the 53 times-capped forward was sin-binned, match commissioner John West has until tonight to decide on any possible citing.
"The same thing happened in a recent game between Bath and Leinster when he
(Grewcock) stepped over a ruck and Guy Easterby was cut on the head,"
claimed Wales coach Mike Ruddock.
"I am not saying it is deliberate or intentional, but it's certainly clumsy.
But regardless of any citing issue, he needs to look at himself - that is the second scrum-half I have seen with cuts to the head.
"I am not going to go too far with the lad. It could just be a clumsy action, and Dwayne had just a minor cut."