Sources allege that Jessica Simpson has warned Jennifer Aniston about John Mayer and his way with women. Mayer and Aniston began dating earlier this month and insiders claimed Simpson, who dated the singer last year, was jealous of the romance.

Insiders now say the 27-year-old, who is currently dating Tony Romo, wants to warn Aniston that Mayer is a “ladies man.”

“Jessica wants Jen to be aware of what she’s letting herself get into with John. She doesn’t want her to make the same mistakes. John is a ladies man,” the source says.

A friend of Mayer’s seems to back up Simpson. “He’ll spend every waking minute talking to someone and spending time with them and then move on to the next girl,” said the friend.