"Fortunately, because the tumour has stayed the same size for a while John's been told that surgery can wait until next year.
"After the operation, he'll need some radio therapy so there's talks of him taking a few months off to get the job done and convalesce."
However, having gone through the same thing in 2012 - when John was diagnosed with a small tumour - he is said to be "a lot calmer", although, it is "emotionally draining" for him.
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The source added: "The first time around John was petrified. But now he seems a lot calmer and I think the fact he's been through this once before is reassuring. He also totally trusts the team where he goes for frequent MRI scans.
"For a while afterwards patients can feel weak, have fits, find it difficult to walk and encounter speech problems.
"Although he's trying to remain as positive as possible it's a really emotionally draining time for poor John."
The Love Me Again star's career peaked recently with the release of his new single Ole with his pal Calvin Harris.
- Bang! Showbiz