Rush said: "Daryl told me he wasn’t going to renew his contract just days after I had taken over because he had an agreement to rejoin his ex-manager at Boston United.
"Daryl’s contract was up at the end of the season but I was willing to appreciate his wishes.
"Daryl has done well for Chester and I was always going to be honest with him. I know his departure will leave us short, but I've now got to look to the future interests of Chester City."