McMillan won't return to Saturday's preseason game at Pittsburgh due to a back injury and also is under evaluation for a concussion, Scott Smith of the Buccaneers' official site reports.
McMillan was undercut while making a leaping grab in the first quarter and landed hard on his neck and helmet. While he remained on the turf for a spell, he was able to walk off the field under his own power before being ruled out. If a concussion is confirmed, McMillan will be subject to the protocol for head injuries in order to practice and eventually see game action again.