According to a story published in The Independent, the Irish golfer decided to end the relationship after Wozniacki posted an embarrassing photo in which he is sleeping with his mouth open while still wearing his glasses.
"Rory was very upset by it and even Serena Williams pointed out -- albeit in a joking way -- it was a pretty mean thing to do," one source told the Irish newspaper.
The source added that the photo was the last straw for McIlroy and that he ended the relationship a few days after Wozniacki posted the image to her millions of Twitter followers. The tennis player is reportedly struggling to accept the split.
"There were a lot of tears. She still has her profile picture on her social-networking site set as the two of them in happier times, but I can tell you the pair are no longer an item," the source said.
The couple, who often defend their relationship on Twitter when rumors like this come about, has been quiet regarding the new report.