Ronaldo commented on the photo on Alvaro Callado's Instagram page featuring his girlfriend Georgina Rodriguez.
Callado and Rodriguez, 22, are seen posing together in the image, leading to a number of people tagging the Portugal captain in their comments on the photo.
Ronaldo then responded with the word 'Cuidado' meaning 'careful' or 'caution'.
Luckily for Callado the response was accompanied by three laughing emojis, making it apparent that the 32 year-old wasn't taking the photo too seriously.
Rodriguez and Collado are former colleagues at fashion label Gucci, with the image suggesting they have maintained a close friendship since she started dating the Real Madrid attacker in November.