Brum face high-flying Nottingham Forest and Larsson knows it will be a test against the Championship club.
"It's a massive competition. For sure, the Premier League is our main focus but we're not going to take the cup lightly and we'll try and do as well as we can," Blues' flying Swede told bcfc.com.
"With confidence being high at the moment we can go there and try and do well but it's going to be an extremely difficult game.
"Forest are flying in the Championship at the moment and it's always extremely difficult as a Premier League team to go to a Championship club because they'll be eager for a scalp. They'll be well up for it and we just have to make sure we are as well."