"I have been surprised, I think everyone has," United's official website quotes the 21-year-old as saying. "I don't think we expected it at the start of the season but they have done really well and hopefully we will be able to break them down.
"They will be filled with confidence after a great win in Dortmund during the week, but this is a different game with a completely different atmosphere. Hopefully Old Trafford will be rocking on Sunday and we will be able to get the three points.
"These are the fixtures you look out for when the fixture list is announced at the start of the season and with Arsenal being in form at the moment, they are probably the team to beat. It will be a difficult game but hopefully we can get the win."
United are currently eighth in the league table.