He'll begin serving it Thursday.
Porcello was initially suspended six games after hitting Zobrist on June 30. He pitched Wednesday night and said before Thursday's game against the Chicago White Sox he was ready to start serving the ban.
The suspension should have minimal effect. Porcello wasn't slated to pitch any of the last four games before the All-Star break, and he'll have to miss only the first game after the break, when Detroit can adjust its rotation anyway.
Porcello is 6-6 with a 4.80 ERA. He says he disagreed with baseball's initial decision to suspend him and was surprised by it.