The Arizona Cardinals and USWNT stars dropped the news on Instagram ... with the two posting photos of Julie's baby bump, and Zach kissing her growing tummy.

"Adding to our starting lineup ... Baby Ertz!" Zach captioned the pics.

The 10-year NFL veteran has been with the U.S. women's national team defender for nearly a decade ... and tied the knot in March 2017.

Of course, Julie was there to celebrate with Zach after Super Bowl LVII, which he won as a member of the Philadelphia Eagles.

Ertz had one of the key plays in the game when he caught what proved to be the go-ahead touchdown from Nick Foles ... propelling Philly over New England in the end.

Julie is a star in her own right -- the two-time Olympian and one-time Olympic gold medalist is one of the most decorated in her position.

Although the baby isn't here yet, having a football and soccer star as parents means the sky is the limit when it comes to sports ... if that's what the youngin' is into, of course.