The 54-year-old revealed that he was unhappy with the striker's contribution during training this week, and told the former West Ham United star that he wanted to see more from him.
"I had a snarl at Frank in training," PA quotes McCarthy as saying.
"I wasn't happy with him and he's shown me what he can do - I told him 'that's the way to show me'.
"I don't take poor performances. You can play badly but put everything in."
Ipswich are 11th in the Championship.