Observed in the locker room after the San Francisco 49ers' 34-3 win over the Houston Texans Sunday night:McDonald worried: Defensive tackle Ray McDonald said he is concerned about a right bicep injury. McDonald said he felt a sting when he was injured. He has a MRI scheduled for Monday. It would hurt the 49ers if he misses extensive time.Staying calm: Defensive players said veterans kept the sideline calm after Tramaine Brock returned a Matt Schaub interception 18 yards for a touchdown on the first drive of the game.