According to RadarOnline, the Total Recall actress is "three months pregnant" and due to give birth in "April 2015".
However, it could be a while until Justin Timberlake and Jessica Biel confirm the family news.
Their insider continued: "Jessica has had tense times in the past when it comes to having a baby, so it is not surprising that she is staying mum on confirming the news publicly yet."
Other news outlets have speculated on Jessica's 'baby bump', with one saying: "Jessica's normally super fit physique has softened a bit.
"While shopping with friends in Los Angeles on October 22, Jessica tried to distract everyone from what appears to be a tiny baby bump by wearing a huge scarf."
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If rumours are true, this will be the first child for the actress, 32, and her Mirrors singing husband, 33, who celebrated their two-year anniversary on 19th October while vacationing in New Zealand.
They marked the occasion by sharing a romantic photo on Instagram during some down time in New Zealand.
Justin captioned the cute shot with a famous quote from Ferris Bueller's Day off, writing: "Life moves pretty fast. If you don't stop and look around once in a while, you could miss it."
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Congratulations to the happy couple, if the baby news is true!