Defender Gregor Robertson has become the sixth Northampton Town player in the last two weeks to leave the club after having his contract terminated.
The 31-year-old joined the League Two club just under a year ago and made 39 appearances.
"We are now looking to move on and it is in Gregor's best interests to move on and play regular football."
Kelvin Langmead, Ricky Ravenhill, David Moyo, Connor Roberts and Sinclair have also left the club this month.
Wilder added: "We are aware the recent exits have left us a little short on numbers, but we do have a couple of additions in the pipeline to boost us.
"Gregor is an excellent professional and he leaves with our thanks and best wishes. It is another tough decision, but a decision made to help take us forward."