Ronaldo removed the two bottles out of camera shot as he sat down for his Euros media conference before holding up his bottle of water and declaring 'drink water'.
The Sun reports Coca-Cola's share price promptly dropped from $56.10 (£39.80) to $55.22 (£39.19).
At one point during the day 1.6 per cent of the company's value had been wiped off - although there was a late recovery, with the price back up to $55.44 (£39.38) at closing.
Ronaldo, 36, has a famously strict diet and avoids sugary foods, eating clean up to six times a day to maintain his incredible physique while he ages.
While still at Real Madrid, the club doctor said he had the body of a player ten years younger and could continue playing at the top level into his 40s.
Ronaldo scored twice for Portugal in last night's victory over Hungary in Budapest.