From MLB.com:

Yankees reliever Scott Proctor dropped his appeal of a four-game suspension on Saturday, opting instead to begin serving his sentence immediately.

As a result, Proctor will be unavailable to the Yankees until a Thursday matinee in Chicago, but he will be reinstated in time for important series against the New York Mets and the Boston Red Sox. ...

But an appeal would have had to take place in New York, and no tentative date for an appearance had yet been set. With that in mind, Proctor said he left the decision up to Torre and general manager Brian Cashman, who informed Proctor of their opinion to have him begin sitting out Saturday.