Jets running back Curtis Martin won't practice when training camp opens Friday because of a lingering knee injury. Martin was placed on the physically unable to perform list Thursday, along with Justin McCareins and Trey Teague. The 33-year-old Martin had arthroscopic surgery last December to clean out his right knee, then was limited during minicamp last month. Though the surgery wasn't considered invasive, it has taken Martin some time to recover. Martin and coach Eric Mangini were unavailable for comment Thursday, when players reported for camp.