APA Group chief executive Mick McCormack could walk away with about $10 million should CK Group's $13 billion takeover of the gas pipeline owner go ahead, after revelations his termination payments have been understated in the annual report for the past five years.

The takeover target on Monday issued a "correction" to its remuneration report, saying it "did not correctly describe the termination entitlements due to Mr McCormack on cessation of employment".