Barton (ankle) was downgraded to out Saturday ahead of Sunday's game versus the 49ers, Josh Weinfuss of ESPN.com reports.
Barton popped up on the injury report Friday due to an ankle issue and was initially deemed questionable for Sunday. However, the injury is severe enough that he's been ruled out with over 24 hours to go before kickoff. Per Bo Brack of GoPHNX.com, rookie Christian Jones is expected to make his first career NFL start Sunday in Barton's stead.