The right-back has played in five pre-season games for the Gills but although Stimson was considering offering the former Charlton man a deal, he has now allowed him to leave the club.
"Sam just fell short a little bit," he said. "I think he needs to go and get some more football and I believe we've got the players in our squad to fill the right-back area."
Striker Moses Ashikodi - who played against Stimson's side in the play-off final for Shrewsbury in May - featured as a Gills XI lost 1-0 at Aveley on Wednesday but he too will not be offered a contract.
"He was mentioned to me last week and I said if he was interested to come along to Aveley and have a game," Stimson added. "He went away to Belgium on Saturday and scored a hat-trick so his agent has been pestering me ever since.
"I've given him a game and you could see he's got something but unfortunately we've got to look better than that."