Cristiano Ronaldo's Pool Hottie Gets Modeling Offer For Underwear

It pays to make out with Cristiano Ronaldo ... 'cause just days after her Miami romp with CR7 ... a huge underwear company wants IG model Casi Davis to take her clothes off ... and put their skivvies on.

The guys over at Ethika Underwear -- a brand rocked by huge celebs like The Game, Nicki Minaj, and Klay Thompson -- fired off a letter to Casi, offering her a spot on their team as a model and brand ambassador.

"After seeing the photos of you and Cristiano Ronaldo, our team did some research and took notice of how into fitness you are ... We think you would fit perfectly with the rest of the major athletes, models and ambassadors we work with."

We called Danny Evans ... VP of marketing for Ethika after we got the letter and he confirmed ... they're totally serious.

"We think she would be a great look for both the performance and lifestyle underwear lines."

GOOOOOOOOOOOOOAAAAAAAAAAAAAAAAAAAL Casi!!!