"The tie is still wide open. We've got to perform very well again to knock Sheffield United out. They've shown what they're capable of today," the Boro said.
"All their players have got Premier League experience and it won't be any easier at home.
"We're pleased to have stayed in the competition because we saw lots of teams go out yesterday. We've got to make sure we keep the run going.
"For everybody that's left in, with only Manchester United and Chelsea of the top four still in there, of course you get that bit closer and it gets more exciting, but we can't really look beyond the replay with Sheffield."