The 32-year-old has been sidelined since October of last year, but is said to be making good progress after his latest operation.
The club's sports therapist Ian Weston told the Gloucester Citizen: "The surgeon found a lot of scar tissue that had been impairing the nerves.
"This had been causing a lot of discomfort and now that it has been removed, John should be able to push on with his recovery.
"The surgeon was very pleased with the results and now we will be targeting a return to full training in mid-August."