manchester united face manchester city in the premier league at old trafford on sunday .
wayne rooney , robin van persie and ander herrera among those in training action .
united have n't beaten manchester city at home in the league since 2001 , losing last three meetings .
van persie has been declared fit to face united 's rivals after returning from nearly two months out .
read : robin van persie is fit for manchester city clash ... but do louis van gaal 's in-form side need him ?