Rooney will go into the match on the back of a brace against West Ham United on Saturday that made him the club's third-highest scorer of all time.
The 28-year-old is also the highest scorer in Manchester derbies, and Moyes believes that the striker's current form will make him a handful for the title-chasing blue half of the city.
"I don't know if he'll be the key man because this game has got many top-class players in it, but he is certainly one of them," Moyes told reporters.
"His form throughout the season has been very good and his goal against West Ham capped it all off. He has a real appetite back again. On Saturday he showed what he is about. He has a big energy back again.
"Everyone who knew Wayne Rooney from old in his early days would say one of the biggest things was that he had big energy and a big heart, and if you get Wayne playing like that, well, the rest of his football takes care of itself."
United are currently seventh in the Premier League table but could move above Everton and into sixth with a win at Old Trafford tomorrow night.