The highly-rated 25-year-old defender swapped Molde for St Mary's in January but has yet to make a first-team appearance for his new club.
Forren's only senior match since the move was Norway's World Cup qualifier against Albania 11 days ago, but international team-mate Hangeland believes he will soon shine in the Premier League.
"We play together for Norway and has done really well," the Fulham defender said. "I think he should be patient and the club should be patient with him. I know he is a great player.
"He is a ball-playing centre-half that can defend and also do something sensible when he has it. He is cut out to be a good player."
- Sports & Recreation