Rangers head for the Riverside Stadium on Saturday having won just two of their last nine Sky Bet Championship games, a return which has seen them slip out of the race for automatic promotion.
But Karanka told Boro's official website: "QPR lost 3-0 against Sheffield Wednesday and played with 10 players after getting a player sent off.
"But if we think they will play like they did in the last game against Wednesday, we are wrong. We need to think of them as a team fighting for the promotion places.
"They were in the Premier League last season and have experienced players and a very good manager, and this makes it a very difficult game.
"We need to think about the game very hard and keep working the way we have been in our home games."