Following nearly five months of feeling unwell, Pledger underwent a series of medical tests, which were inconclusive.
He was admitted to hospital last week after becoming ill and specialists made the diagnosis.
They believe he may have been battling the condition for a long time.
Pledger is optimistic, however.
"Obviously, this has been a shock. Early tests are showing positive signs and I’m feeling really good about our plan to beat this.
"I feel extremely lucky that this has been discovered at the stage that it has.
"I’m really grateful for the medical team, my family and the wonderful support I’m already receiving from the basketball community.
"I’m looking forward to the future and hopefully getting back on court."
The Southland Sharks say Pledger will remain an integral part of their playing roster for the 2021 s NBL season.
