Gillingham boss Neil Harris says his players will write their names in FA Cup folklore if League Two's bottom club beat Leicester City.
The Foxes, winners in 2020-21, are strong favourites to reach the fourth round against opponents who have not won a league match since 1 October.
The tie is live on BBC One and Harris said: "These games are made for heroes.
"People are going to tune in to see if Gillingham can cause one of the biggest upsets of all time."
Gillingham are five points from safety in League Two, but Harris said Saturday's tie is not a distraction from trying to stay in the Football League.