Sanders had been listed as questionable.
The source said Sanders is progressing well but that the team wants to make sure he is good to go for the long haul, leading to the decision to keep him out Sunday.
Sanders had been listed as week-to-week with a lower-body injury in August.
The 23-year-old set team records for scrimmage yards (1,327) and rushing yards (818) by a rookie while finishing eighth in the NFL in all-purpose yards (1,641) last season. He did all of that despite starting the season as the No. 2 back behind Jordan Howard and playing 53% of the offensive snaps.
The Eagles intend for Sanders to be their primary back this season.
ESPN's Tim McManus contributed to this report.