Manchester United have been alerted amid speculation that Cristiano Ronaldo and Sergio Ramos have asked to leave Real Madrid, according to Sport.
The two players have both been linked with a move to Old Trafford in the past and could now be the subject of another transfer attempt from the Premier League giants.
It is believed that they approached club president Florentino Perez in order to discuss the terms of their potential departure during the upcoming window.
Ramos was heavily linked with a switch to England during the summer, but instead decided to stay after being given a new deal at the Bernabeu.
Ronaldo has constantly been linked with a return to his former club after leaving Manchester for the Spanish giants back in 2009 and becoming a huge success.
It is now unsure whether United will reignite interest in Ramos, but could be interested in a move to bring back Ronaldo, who is also being targeted by current Ligue 1 champions Paris Saint-Germain.