England clash with Norway on Wednesday night in a friendly that is expected to produce a record-low attendance at Wembley following the national team’s dismal World Cup.
But Forren, who played for Southampton last season, stoked the flames over the new England skipper’s weight – an issue that has dogged him previously in his career – and suggested there will be minimal friendliness from their part.
"We know we're a good team so there's no reason for us to walk around thinking we can't stop them," Forren said.
"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.
"It’s almost a bit scary looking at their forwards 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.
"Rooney looks a bit chubby."
England boss Roy Hodgson has included three uncapped newcomers in a squad he will cast one final eye over before their first Euro 2016 qualifier against Switzerland on Monday.
Calum Chambers, Jack Colback and Danny Rose have made the cut following the retirements of Steven Gerrard and Frank Lampard, but they are not expected to start against the Norwegians.
Norway are 53rd in the FIFA world rankings, 33 spots below England in 20th, and last reached the European Championship finals in 2000.
This time around they have another difficult task to qualify from their group, which includes Italy and Croatia.