Frank Ribery, the Bayern Munich winger, is the most obvious choice to replace Cristiano Ronaldo. However Bayern have already rejected Real Madrid's advances and the value they have placed on him, more than £50m, could be too much for Manchester United, notwithstanding the £80m they will receive for RonaldoPhotograph: Alexander Hassenstein/Bongarts/Getty ImagesLosing Ronaldo is like losing two players - an electric winger and a goalscoring striker. If Sir Alex Ferguson is looking for a new version of the latter, Valencia's David Villa is on the market, although Real Madrid are expected to win the race for his signature tooPhotograph: Diego Tuson/AFP/Getty ImagesSergio Aguero is another who could offer Ferguson a real threat up front, but Atletico Madrid are loathe to sell their prime asset. United would face competition from Chelsea and Manchester City if the Argentine does become availablePhotograph: Jasper Juinen/Getty ImagesDouglas Costa seems to fit the bill perfectly. Like Ronaldo he can play through the middle or on the wing, and he is also a brilliant taker of free-kicks. The 18-year-old Gremio forward has a buyout clause of €21mPhotograph: Juan Barreto/AFP/Getty ImagesAntonio Valencia is the player Ferguson is most likely to bring in, the £16m Wigan winger a long-term target. Pacy and skilful he ticks most of the boxes, although he is yet to prove himself as a goalscorer in Ronaldo's leaguePhotograph: Ivan Alvarado/ReutersThere are no such worries over Karim Benzema, Lyon's brilliant young centre-forward. Although he is yet to really prove himself with France, Ferguson has held him in high regard for a few yearsPhotograph: Daniel Mihailescu/AFP/Getty ImagesJavier Pastore is the much-loved star of Huracan, a gifted attacking midfielder who does not shirk the physical side of the game. He is highly regarded in Argentina, although Diego Maradona refused to call him up recently to the national teamPhotograph: Alejandro Pagni/AFP/Getty ImagesNilmar is one of the brightest prospects in Brazilian footballer. After spending an unremarkable spell at Lyon, the striker has rediscovered his scoring touch with InternacionalPhotograph: Bruno Domingos/Reuters