Northampton are one of a number of former clubs for the 34-year-old centre-half, whose prevous spell at Sixfields was blighted by injuries.
Hailing the player's fitness levels as those of someone 5 years younger, Cobblers boss Gary Johnson told BBC Radio Northampton: "He's a decent, experienced player.
"He's here for a month, unpaid, and we'll see how he goes. But I've liked what I've seen."