Advertising veteran John Singleton has signed over his stake in Macquarie Media with his friend and venture capitalist Mark Carnegie expected to follow suit, delivering Nine Entertainment the shareholding it needs to seal the takeover of the radio broadcaster.

Nine lifted its stake to 87.05 per cent on Tuesday morning, up from 54.4 per cent, after Mr Singleton accepted Nine's $1.46-per-share offer. Sources have indicated Mr Carnegie is likely to back the offer following an independent expert's report by PwC that declared Nine's offer fair and reasonable.