Iker Casillas' agent "has been in contact" with Tottenham Hotspur and Arsenal, among other clubs, as Real Madrid speed up negotiations to sign Manchester United goalkeeper David De Gea.Carlos Carpio of Marca reports "as more time passes, the De Gea deal gets more expensive" for Los Blancos. He also notes United are "offended" by the agreement already put in place between their goalkeeper and the Spanish club, and that a figure "ofno less than 30 million (approx. 21.3 million)" is needed to prise him away from Old Trafford.This could have huge ramifications for Spurs, who, according to French publication L'Equipe (h/t Neil McLeman of the Mirror), have given Hugo Lloris a "verbal agreement" he can leave if a 25 million (17.8 million) bid comes in.United are linked with signing the Frenchman as a replacement for De Gea, as reported by Richard Parry and Tom Collomosse of the London Evening Standard. This could make Casillas' possible switch to White Hart Lane the final piece in a transfer carousel involving the three clubs.Carlo Cutropia, Casillas representative, "has been in contact with the clubs that over the last few weeks have shown interest in employing his services," according to Carpio.Despite appearing on the brink of signing Chelsea icon Petr Cech, as reported by David Ornstein of BBC Sport, Arsenal are mentioned alongside Spurs.French champions Paris Saint-Germain, plus Serie A sides Inter Milan and Roma are also touted to make an approach for Casillas. Although Turkish clubs Fenerbahce and Besiktas are mentioned, Carpio notes "playing in a lesser league does not interest Casillas." He is also not willing to remain in Spain unless he's at the Bernabeu.Spurs boss Mauricio Pochettino will need to find a suitable replacement for Lloris if he does leave. However, it's easy to forget the club possess a more than capable alternative in Michel Vorm.The Dutchman earned his move to north London after starring for Swansea City in the Premier League, but he made just four Premier League appearances last season. These were brought on by Lloris picking up an injury, per WhoScored.com.Casillas is a proven winner who has suffered a downturn in form over the last few years. The 34-year-old hasn't been able to put together a run of consistent quality since former Madrid boss Jose Mourinho dropped him in 2012. It would be tasty to see Casillas face the current Chelsea boss in England.B/R UK's Guillem Balague recently discussed the difficulties Casillas will face when he departs Madrid:Losing Lloris would be disappointing for Spurs, particularly as his sweeper-keeper style is difficult to replicate with such quality. Casillas isn't the type to rush off his line and dive into tackles. He was a commanding force and excellent shot-stopper in his prime but needs confidence to reach this level again.If (or when) De Gea moves to Madrid, it's likely Casillas' reign as Spain's No. 1 international goalkeeper will also come to an end. No player proved more pivotal to United's Champions League qualification during the recently concluded campaign, and at 24 years old, De Gea is ready to take on greater responsibility.This is likely to see a rejig at three of the continent's biggest clubs, with Spurs being pulled into a situation which is beyond their control.The north London side have a "special partnership" with Los Blancosone which has seen Luka Modric and Gareth Bale sold to Madridso Casillas' arrival could finally help Spurs get a return on their decision to hop into an odd, uneasy relationship with the Spanish powerhouse club. Click here to read full news..