According to Page Six, Vergara was seen wearing a diamond ring during their romantic vacation on the tropical island.
An E! News source stated that Manganiello asked Vergara to marry him on Christmas Day.
“I’ve never seen two people so truly in love,” a source told the site about the couple. “The way they talk to each other, touch each other. It’s incredible.”
On Sunday, the Modern Family star shared a cozy picture of them with a sweet message for Manganiello’s 38th birthday.
“Happy happy bday to my love and best friend to the one that makes me laugh like crazy!have a healthy wonderfull year babe!!!” she wrote.
The couple, who has been dating since July, is yet to confirm the happy news.