That's the view of former centre-half Guy Branston, who represented both clubs during his career.
Wednesday are under huge pressure right now, having won just once in their last eight games.
Ahead of the Hillsborough tussle, Branston says Wednesday's players need to stand up and be counted.
He says that if they don't then they risk becoming the first side to lose at home to Rotherham at this level in 36 matches.
"You can change your identity as a player if you turn up and perform in these," Branston told the Star.
"Wednesday have massively under-performed so far.
"Some of the players that have been there for quite a while are just not delivering as they should be.
"There are players who should be doing better.
"But Wednesday are reeling at the minute and the pressure is on them.
"Defensively, they aren't the best and if Rotherham catch them off-guard and if they can get about them, I can see them (Rotherham) turning them over."
Branston, now coaching the youngsters at Leicester City, only played in the fixture once whilst at United and says the occasion is one that players should relish.
"I only played in this fixture once, and that was a friendly when I injured Lee Bradbury!", said Branston.
"As a player, you love to be involved in games like this.
"It's an unbelievable occasion."