http://profootballtalk.nbcsports.com...chargers-camp/

Michael Gehlken of the Union-Tribune San Diego confirms that Gaither’s back is “healing slower than the Chargers hoped.” Gaither will not play in the Chargers’ exhibition opener, and “there is some doubt” about his availability for the second week of the preseason.
May not mean much in the long run, but it's a pretty bad coincidence that he's struggling with his back again after getting paid.