The Norway international moved from St Mary's Stadium from Molde earlier this month, but is not expecting to just walk into Mauricio Pochettino's side.
Forren admits that the Premier League is a big step up from Norway's Tippeligaen, but is confident that having featured in Europe will help him adapt.
"I'll fight for that and train hard, then we'll see if I'm in the squad," he told reporters. "To make my debut at Old Trafford would be perfect, but I'm patient because I know it's hard to just come here.
|PREMIER LEAGUE PREVIEW
|12/1||Southampton are 12/1 with bet365 to beat Man Utd at Old Trafford this week
"You have to show you're good enough, so I'll train hard and get my chance when I'm ready.
"The Norwegian league isn't as good as this one, but it's at a high level..
"Playing in the Europa League, Champions League qualifying matches and for the national team has helped me believe that I am good enough for this and being able to take the next step.
"I feel ready to play in the best league in the world, and I'm very happy to be here.
"For me, it's always been a dream to play in the Premier League."