Rooney was unveiled as the new England captain last week despite an underwhelming performance at this summer's World Cup, which saw the striker score only one goal.
Norway are placed 53rd in the FIFA world rankings, 33 spots below England, but Forren insists he will not be afraid of his opponents at Wembley.
"Rooney looks a bit chubby," Forren told TV2.
"They're obviously good players, and many of them are on good form already after three games in the Premier League but we're looking forward to it."
The match will give Roy Hodgson a final chance to see his players in competitive action before England begin their Euro 2016 qualification campaign in Switzerland on Monday.
Norway last reached the finals of a European Championship in 2000 and the Scandinavian side face a difficult task to qualify from a group that includes Italy and Croatia.
"It's almost a bit scary but it's in games like this and experiences like this you want to be able to contribute so I'm looking forward to it," Forren said.
"We know we're a good team so there's no reason for us to walk around thinking we can't stop them."
Forren joined Southampton in January 2013 but returned to Norwegian side Molde six months later, having failed to make a first team appearance at St Mary's.
The 26-year-old defender was linked with a move to Cardiff this summer but says he is happy at his current club.
"I'll be staying in Molde for the rest of the season," Forren said.
"We're enjoying ourselves at the moment and we want to finish the season in the best possible way. I'm very happy I get to be a part of that."
- Sports & Recreation