The singer - who got engaged to the NFL player on Thursday (11.11.10) after six months of dating - is said to have caused problems with her father Joe, who also acts as her manager, by refusing to draw up an agreement deciding how the couple's wealth and assets would be divided should they separate in the future.
An insider explained: "At the moment, Joe is sitting back and being a great father supporting his daughter and his future son-in-law.
"However, you can bet after all the excitement has died down, Joe is going to do everything in his power to make sure Jessica doesn't walk down the aisle until Eric signs away any right he might have to Jessica's enormous Fortune."
Friends of the 30-year-old star - who is believed to be worth around $100 million - are also said to be worried her future spouse could end up with a substantial amount of her cash after Jessica's ex-husband Nick Lachey took $10 million of her fortune when their divorce was finalised in June 2006.
The source added to website PopEater: "Nick walked away with over $10 million of her money when they divorced, because they had no prenup. You would think she would have learned her lesson. But where romance is concerned, Jess follows her heart not her head."