The 39-year-old former Champions League winner has been given the number 38 shirt as he dusts down his boots to return to first-team action in the less glamorous surroundings of Underhill.
Davids had been out of football since a brief stint at Championship side Crystal Palace in 2010, until joining Mark Robson in the Barnet dug-out last week.
His arrival at the club failed to spark a revival of fortunes for the Bees, as they lost 4-1 to Plymouth last weekend to remain as the bottom team in the Football League.
Northampton have a doubt over right-back Danny East so Chris Hackett is likely to continue in the role.
Ben Harding, David Artell, John Johnson and Luke Guttridge are all out.