The 23-year-old former Bristol City man is the 12th player to have left since Tim Harris and Marc Richards came to the club.
Richards said that Murphy made the decision to leave after realising he wasn't going to be in squad.
"He realised he wasn't going to be in the squad, I think it was Boxing Day or the Chester game," Richards said.
"He decided to part company and we're not going stand in anyone's way."
Richards said that Murphy made the decision to leave after realising he wasn't going to be in squad.
"He realised he wasn't going to be in the squad, I think it was Boxing Day or the Chester game," Richards said.
"He decided to part company and we're not going stand in anyone's way."