Cobblers will continue to monitor young defender Camron McWilliams during pre-season after he played 45 minutes at Sileby on Saturday.
The 20-year-old defender, younger brother of Shaun, came through Northampton's youth system but left the club to join Cardiff last year.
But, after being released by the Bluebirds in May, he made a surprise appearance at left-back for Town during the second-half of Saturday's opening pre-season at Fernie Fields.
Explaining the situation, manager Jon Brady said: "I track all the young boys who have been in and around myself over the last few years.
"I worked very close with Steve Morison and at the time he was my assistant in the youth team before he went on to do the U23s at Cardiff.
"He took Camron with him because he liked him and it was a good opportunity for Cam, but he's been released by Cardiff and at the moment he's a free agent.
"I've kept tabs on him and he's come back very strong and very fit and like all of the McWilliams boys, they can run and they're very robust.
"But for Cam, it's about keeping his fitness up because in the past he's broken down through injury. Hopefully we can get some consistency out of him and see how he does during pre-season."