Manchester United welcome Manchester City to Old Trafford on this season . Sergio Aguero has scored six goals against Man Utd since joining City . Radamel Falcao says the Argentine is the main threat for Man United . Falcao is hoping to make his first appearance in a Manchester derby . Colombian says he is happy at Man Utd despite bit-part role Sunday .
Manchester United welcome Manchester City to Old Trafford on Sunday . Sergio Aguero has scored six goals against Man Utd since joining City . Radamel Falcao says the Argentine is the main threat for Man United . Falcao is hoping to make his first appearance in a Manchester derby . Colombian says he is happy at Man Utd despite bit-part role this season .