Stoke City manager Tony Pulis has condemned Marouane Fellaini for his headbutt on centre-back Ryan Shawcross.
The Belgian has since apologised for his actions, which went unpunished at the time.
David Moyes had already voiced his opinion, stating that Fellaini "deserves" punishment.
"I have a lot of respect for Mark Halsey (referee) and I think he's a good referee, but I don't know whether he has seen it," Sky Sports News quotes Pulis as saying.
"If he has seen it and not acted, then you really want to know why he has not acted.
"I don't think you can hide behind anything and what [Fellaini] has done is wrong."
The game ended 1-1 at the Britannia Stadium.
