"Joey went in (Wednesday) morning for an MRI after having swelling develop overnight," said Steelers Coach Bill Cowher. "After reading the MRI, he had a loose cartilage body in there and Dr. (James) Bradley had to remove it.
"Joey had the arthroscopic surgery (Wednesday) afternoon, and his time frame is about four weeks," Cowher added. "He'll miss the pre-season, and hopefully we'll have him for the opener."
Porter, who was selected by the Steelers in the third round of the 1998 NFL Draft, suffered the injury during a one-on-one pass-rush drill Tuesday afternoon at the Steelers' training camp at St. Vincent College.