Manny has priors too, so he probably won't get off with just a slap on the wrist. He's done his fair of thuggish stuff and the whole incident was just ugly - if the ref had called the foul against O'Donovan originally for being all over Manny then the arm swing and headbutt wouldn't have happened.
He did. And actually, Manny swings his arm after the whistle had gone for the foul.
Pretty sure that Manny takes the free kick, passes it to Durante, and then jogs over to O'Donovan (who was walking away) for the headbutt.