The actress - who is dating Justin Timberlake - admits she and the 'Pretty Woman' star bonded instantly on the set of their new movie 'Valentine's Day' and can't bear to be out of contact with one another.
She said: "I hear she has a girl crush on me and I definitely have one on her. I think she is amazing. Although I did panic for a while because I sent her a text and she didn't reply for a while. But we're fine now."
The 27-year-old star - whose romance with Justin has been the subject of much speculation that it is on the rocks - also claimed to have no plans to celebrate Valentine's Day (14.02.10) with the singer because she is too busy with work.
However, she added: "I love Valentine's Day! It's great to take a day out and celebrate loving and caring for people... It's great!"
As well as her feelings for Julia, Jessica has previously admitted to having a crush on another of her female 'Valentine's Day' co-stars.
Speaking about Jennifer Garner, she said recently: "My girl crush is Jen at the moment but here's the thing with girl crushes - it's more of a respect thing. It's like, you're beautiful, you're cool, you look and seem like somebody I would want to hang out with and your career is awesome."