Last season's top scorer is unlikely to feature again this campaign after picking up an injury against Olympiakos and, with Van Persie sidelined, Juan Mata and Wayne Rooney combined to good effect to beat West Ham on Saturday.
Moyes, though, says that the former Arsenal man would be coveted by any club in Europe and reiterated how great a loss the 30-year-old will be - though he is confident that Mata has the ability to step up and deliver while Van Persie is out of action.
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"Mata came here to play two or three positions. We knew that. You're never going to go through a season with no injuries. I mentioned that in one of my early press conferences, that players would get injured and you won't always have Wayne Rooney or Robin van Persie fit for every game.
"That's why you need a squad of players and Juan has come in and played well. He played very well on Saturday – he's done well in all the games but, on Saturday, he was closer to scoring himself and maybe should have done on a couple of occasions."
United take on rivals City at Old Trafford on Tuesday and, with the club languishing in seventh place and having lost five times at home this season already, Moyes is keen to repay fans with a big performance in the derby.
"I think we want to try and perform better in the bigger games than we have done, no doubt about that," the former Everton boss continued, "but we want to win all the games and we won't go into this one any different.
"It's important for us to show the level we have got. We have got the level and we're not as far away as many people would have us. I've got no doubt it will improve but we want to show we're still in there fighting."