Cornes, 33, was sent south to Victoria by Giants officials to address his knee troubles which they had been monitoring during the pre-season.
Giants sports science manager John Quinn said the results showed the seasoned premiership player needed an operation and significant recovery time.
"We decided to send Chad to Melbourne to meet with Dr David Young to investigate the cause of his knee issues," Quinn said on gwsgiants.com.au.
"They discovered a cyst on Chad's right knee and decided the best cause of action was to operate. They're very happy with the results."
Cornes played 16 games for the Giants in their inaugural season last year, after crossing from Port Adelaide where he made 239 appearances.