Sami Khedira shouldn't want to leave Real Madrid, but if José Mourinho's Chelsea is behind the offer, he could think otherwise. According to 'Sport', Florentino Pérez and Zidane are interested in signing French midfielder Geoffrey Kondogbia away from Sevilla, and the deal could be completed quite soon.
Furthermore, 'Sport' believes that there's an 18M€ offer from Chelsea to sign Khedira. That doesn't seem to be a fair price, so Khedira's potential departure is not very likely right now.
Real Madrid could likely sign Kondogbia for almost 15M€, so selling one of Germany's starters for almost the very same price would make no sense unless Khedira is unhappy.
Kondogbia is a fine prospect but he's not as polished as Khedira, as he showed in the U20 FIFA World Cup that he won with the French U20 team that also featured Sanogo, Pogba and Digne.
This rumor should be taken carefully. German site Transfermarkt and ITV also reported the news quoting Sport's information.