"They broke up recently," a source close to A-Rod told the magazine.
The source said that the 39-year-old star of films such as "There's Something About Mary" and "Bad Teacher," is "very busy with her career," while Rodriguez, 36, has "had injuries and wants to focus on his game."
"They're dedicated professionals," said the same person, adding that the actress and ballplayer are "still very friendly and like each other."
The couple have already gone through several breakups during their relationship, the last one in June, after which they reconciled.
Rodriguez, who divorced his wife Cynthia in 2008 and who then began a relationship with singer Madonna, began going out with Diaz a year ago, when he decided to celebrate his feat of becoming the youngest ballplayer in history to hit 600 homers by taking a helicopter ride over New York accompanied by her and her friend Gwyneth Paltrow.