David de Gea
David de Gea will travel with United overseas in the strongest hint yet that he will remain Getty Images

Real Madrid can sign Manchester United star David de Gea only if they include Sergio Ramos as part of a swap deal, according to the BBC.

The 24-year-old is part of Louis van Gaal's side in the United States, while the defender is in Australia with the Spanish capital club. Both players have travelled with their teams for the pre-season tour.

The United goalkeeper has one year left on his contract and has already rejected a chance to sign a new deal. The former Barcelona and Bayern Munich manager hinted that De Gea may join the 10-time European champions.

The Premier League giants are willing to hold on to their player and let the stopper leave for nothing after the end of the next season. This will see United lose around £25m ($39m) if they allow De Gea to leave on a free transfer in the summer of 2016.

United are aware that De Gea will not commit his future to his current employers beyond 2016. The English side are adamant that the keeper can join Real only if Ramos is allowed to move in the opposite direction.

Spanish newspaper AS claims United are keen on bringing Ramos to Old Trafford in the summer transfer window. The 29-year-old defender has two years left on his contract at Santiago Bernabeu.

Real manager Rafael Benitez reiterated his and the club's desire to retain Ramos and not let him leave the Spanish outfit this summer. The central defender is open to the idea of leaving his current employers and join United.

United have already seen their two bids for Ramos being turned down by Real. The two-time United Player of the Year is the La Liga giants' primary summer target, especially after they allowed Iker Casillas to join FC Porto after 25 years of service.

However, Real completed the signing of Kiko Casilla from Espanyol on 17 July. They now have the services of Casilla and Keylor Navas as the two keepers in the squad. After Casillas's exit, Real made Ramos the new club captain but the contract talks have stalled, according to Marca.

Real are keen on retaining Ramos and then signing De Gea, while United are adamant they will only do business if there is a swap deal on the table.