Harrad, 34, finished a month-long deal with the Gingerbreads on Saturday after an injury plagued year, but has expressed a desire to leave Matlock for pastures new.
Manager Dave Frecklington and Chief Executive Keith Brown both paid tribute to Harrad who also had a spell as assistant manager to Dave Hoole with the Gladiators before Hoole left by mutual consent in September.
Frecklington said: "Shaun expressed a wish to leave which we accepted, it's one of those things which happen in football and we move on.
"We're parting on good terms, there's no hard feelings. Unfortunately Shaun's been hampered by injury in my tenure at the club but he's always been the model professional in my dealings with him. He helped us tremendously when we first arrived and I've nothing but high praise for him and I wish him well wherever he goes."
Harrad missed the final six weeks of last season due to an ankle operation and initially had a spell as assistant caretaker boss with Hoole after Glenn Kirkwood and Craig Hopkins left the Gladiators towards the end of March. Matlock had a good end to the season, winning six and drawing two of their final ten matches leading to Hoole being appointed and naming Harrad as his assistant on a permanent basis.
He scored twice in an opening day 4-0 win against Lancaster City before adding further goals against Gainsborough Trinity and Halesowen Town but in the Halesowen game, Harrad picked up another injury, cracking his tibia in a collision with the opposing goalkeeper.
Under Frecklington, Harrad managed a brief substitutes appearance setting up Matlock's final goal in a 3-1 home win against Stalybridge Celtic in November prior to his spell at Grantham where he scored twice.
Harrad joined Matlock in the summer of 2017 after a long career in both the Football League and Conference.
He began his career at Notts County and also played for the likes of Northampton Town, Rotherham United, Bury and Cheltenham Town as well as helping Burton Albion into the Football League in 2009. He was Matlock's top scorer last season.