SANTA CLARA, Calif. – Earlier Wednesday, San Francisco 49ers coach Jim Harbaugh said it was possible the team will add to its thin defensive line this week in the form of a roster move.After practice, it became evident why such a move could happen. Starting defensive linemen Justin Smith (shoulder), Ray McDonald (biceps) and Glenn Dorsey (hamstring) all did not practice.Smith and McDonald are likely to play Sunday at Tennessee, although McDonald is still getting used to playing with his injury he suffered in Week 5.