The former Spennymoor man sustained the blow during the club’s recent pre-season friendly against Dunston UTS.
He has been with the Highwaymen since May 2020.
Discussing the injury, Morpeth Town head of sports science and medicine Steven Shaw detailed the next steps for Johnson.
“AJ suffered a full rupture of his AC Joint which needed work done straight away to secure the joint," he told the club's official website.
“It had some metal work and strong sutures which secure the ligaments while they repair naturally.
“Unfortunately, this requires another surgery to take the metal buttons out when they are happy the ligament has healed sufficiently.
“The problem with that is it’s not easy to timeline. Every person’s healing properties are individual to them; you can do things to help like taking collagen supplements, but the most important thing is it’s not rushed because the ligaments need time to mature and that can take more than six months and in some cases more.
“However, he’s been given a loose estimate of 4-6 months, based on his current athleticism.
“AJ is in good shape and works hard in the gym so you can guarantee he will go back in for that second surgery as quickly as possible, but he still has to be cautious and patient and allow the healing process to happen.”
Photo Credit: Morpeth Town