Celebrity news site Page Six reports that a source said Mara 'may be as far as six months along in her pregnancy'.
Photos published by some outlets show Mara wearing baggy clothes, with some speculating that this could be to 'cover her bump'.
Joaquin and Rooney
Reports about when the couple started dating, and whether they are engaged - are inconsistent, which is unsurprising as the pair are notoriously private.
Page Six reports that the couple - who often engage in vegan advocacy together and separately - first met in 2013, on the set of Spike Jonze film Her, and began dating in 2018 after acting together in the movie Mary Magdalene.
Some reports say they got engaged in July 2019, based on Mara being snapped wearing a ring on her engagement finger, with others saying the couple will never marry, as they believe 'marriage is too mainstream'.
Numerous outlets have reported reaching out to reps for both Mara and Phoenix, who have not yet commented on the news.