Head coach Steve Cooper says Nottingham Forest must "believe" if they are to upset FA Cup holders Leicester City.
Forest knocked out Arsenal in round three and now host their East Midlands rivals in Sunday's fourth-round tie, which is live on BBC One (16:00 GMT).
"Anything can happen," Cooper told BBC Radio Nottingham.
"As long as you believe in yourselves you can win any game but you have to do that - believe in yourselves, play well and put the right plan together."
Forest, whose captain Lewis Grabban has been ruled out for two months because of an ankle injury, will be backed by a sold-out City Ground as the two sides meet in the cup for the first time in 10 years.