Steelers offensive lineman Darnell Stapleton sat out both practices again on Tuesday with an injured left knee. Stapleton reportedly had an MRI on the knee on Monday and head coach Mike Tomlin stated after practice that they are still looking at the injury and no results were released. Stapleton was seen in between practices without a brace on the knee. Stapleton had worked early on in training camp as starting center Justin Hartwig continues to rehab his injured toe. 2008 practice squad center Doug Legursky and rookie A.Q. Shipley have been taking the snaps at center in their absence. Stapleton is fastly losing ground to fellow offensive lineman Trai Essex for the starting right guard position.