Roger Federer-Stan Wawrinka Rift: Back Injury or Wawrinka Ire Toward Wife Ruining Federer's Davis Cup Hopes? [VIDEO]

Roger Federer insists that it was his back -and not his wife's heated conversation with Stanislas Wawrinka at last week's ATP World Tour Finals in London - that remains bent out of shape as he tries to prepare for the Davis Cup final for Switzerland against France starting Friday.