The 31-year old has had an extensive career in England, beginning in 1995 with the Red Devils, before having stints with Barnsley, Blackburn Rovers, Sheffield United, Leicester City, Portsmouth, Preston North End, Nottingham Forest, Queens Park Rangers, Wrexham and Northampton Town.
Curtis is a versatile defender and will spend the next fortnight training with the second-year club with coach Miron Bleiberg keeping the door ajar for a contract if things go well.
"John is very welcome to come and spend some time with us and we are very much looking forward to having him here," Bleiberg said.
"He has undoubted quality and is very experienced. John is coming here via a mutual acquaintance and I am not sure at this stage what his long-term intentions are.
"Anything is possible, but the plan at the moment is for John to come and train with us and we will see what happens from there."