The pair are close thanks to their days together at AC Milan.
"I've told him not to forget that winning alone isn't enough in Spain. Carlo is a good, intelligent person who knows football and understands that Real is the most famous club in the world. It's an honour and a source of pride for him, but the same goes for Real Madrid," Sacchi said.
"He's a winner as a coach, but his teams don't just get results – they play football the right way, too. When Florentino Pérez asked me about him, I told him he shouldn't think twice about signing Carlo."