Sir Alex Ferguson has put together a list of potential summer transfer targets as he tries to fill the enormous void created by the imminent £80m transfer of Cristiano Ronaldo to Real Madrid and the ­prospect of Carlos Tevez following the world ­footballer of the year out of Old Trafford.

Manchester United's first response to sanctioning Ronaldo's departure will be to follow up their interest in Luis Antonio Valencia and offer around £17m to Wigan Athletic. Ferguson is also an admirer of Karim Benzema and will investigate the cost of signing the France striker from Lyon, particularly if Tevez goes through with his threat to leave. Jean Michel Aulas, the Lyon president, has stated that Benzema will not leave for less than €80m (£68m), but it is thought the French club would actually sell for half that amount.

United are also monitoring Franck Ribéry's availability, although the Bayern Munich player would prefer to move to Spain and, with the Valencia striker David Villa, is another target for Madrid in what is shaping up to be the most remarkable period of transfer spending in history.

Having already signed Kaka from Milan for £59m, the capture of Ronaldo will be the culmination of 18 months of strategic planning on the part of Madrid and the player. The club expect Ronaldo to arrive in Spain "in the next few days" and the deal will be concluded as soon as he has passed his medical examination. His ­salary was agreed almost a year ago, when Madrid put the deal in place. Ronaldo will earn a flat wage of £6.8m a year plus substantial add-ons and image-rights payments.

"This is very flattering for me," Ronaldo said last night. "The fact that two of the world's greatest teams want to trade me is not something that happens every day."

Ronaldo, currently on holiday in Los Angeles, also confirmed that a doctor from Madrid had examined the groin injury that has been troubling him. "Every­one wants to see and test your product or future product," he explained. "It does not require an operation."

The announcement from Old Trafford yesterday represents a devastating blow for the Premier League champions and is the news their supporters have been dreading ever since Ronaldo began ­talking openly of his "dream" to join Madrid. He tried to force through a transfer this time last year. Ferguson persuaded him to stay at Old Trafford for another year but ­Ronaldo made it clear that it would be his final season with the club.

His agent, Jorge Mendes, worked out a deal with all the relevant people as long ago as last September, writing in various pledges and confidentiality clauses.

"Let's just say that everyone involved in the operation agreed to do it this season," Ramón Calderón, Madrid's president at that time, said last night. "That is what I can say. Last season United decided not to do it because they thought it was too early and instead everyone agreed to do it this season. He [Ronaldo] wanted to come, he said that many times. It's OK for Real Madrid and also for Manchester United, who will get a lot of money."

United's official stance was that Ronaldo would not be allowed to leave, something the club's chief executive, David Gill, repeated as recently as two weeks ago. Ferguson went even further in his own denials, declaring last December that he would not sell "that mob a virus".

Instead, the deal was tied up in a 15-minute telephone call on Wednesday, when Madrid's new president, Florentino Pérez, contacted Gill to tell him the money was in place. Mendes had already let United know his client still wanted to leave and Gill interrupted Ferguson's holiday in France to inform him. The club released the news in a statement: "Manchester United have received a world-record, unconditional offer of £80m for Cristiano Ronaldo from Real Madrid. At the request of Cristiano – who has again expressed his desire to leave – and after discussion with the player's representatives, United have agreed to give Real Madrid permission to talk to the player. Matters are expected to be concluded by 30 June."

That leaves Ferguson with the task of replacing the potentially irreplaceable but his priority will be to persuade Tevez, a free agent from 30 June, to resist ­Manchester City's offer of a huge pay rise and a regular first-team place. Tevez has become disillusioned about the way he perceives he has been treated at Old ­Trafford, but Ferguson has broken off from his holiday on several occasions over the last week to contact the Argentina striker. Nonetheless, Tevez is aware that United are trying to sign Valencia and has not received any assurances about playing more regularly if he were to stay.

Uefa's president, Michel Platini, last night described the bid for Ronaldo as "excessive", adding: "It is very puzzling at a time when football faces some of its worst ever financial challenges. These transfers are a serious challenge to the idea of fair play."