The Denmark international is discussing a £3million switch to Craven Cottage and is expected to sign a three-year contract.
"I am looking forward to a new challenge," said Andreasen in Bild.
"The desire for a change has been with me since the summer."
Bremen's sporting director Klaus Allofs has confirmed that the German side have accepted Fulham's offer for the 24-year-old.
Allofs said: "The offer was attractive and Leon is not happy with us."