Mourinho is continually being linked with a move away from Madrid at the end of the 2012-13 campaign, but the former Inter boss has so far denied rumours that he could leave the club.
"I don't know whether the time has come for Mourinho and Madrid to part company this summer. Winning only the Copa del Rey with this team will not be enough for Real Madrid," Santillana told Goal.com. "However, if the team bounces back and manages to win the Champions League, I don't think that Madrid should let him go."
The 60-year-old also had his say on Cristiano Ronaldo and had nothing but praise for the prolific attacker.
"Cristiano is a great player and one of the best in the world. He has incredible natural abilities, spectacular physique, great height, fantastic fitness, speed. He really has everything. He's a freak of nature," Santillana explained. "He doesn't need any tricks to get a chance inside the area. I did, because I'm smaller, I needed to anticipate the defenders, but he can outjump his rivals. "
He added, "He is also a great header of the ball, not a specialist, but he does very well. And not only that... He is fast, shoots with his right leg, with his left leg. He has it all! If he doesn't get injured or leaves the club - and I hope he doesn't - he will break all the club records. Just like [Lionel] Messi in Barcelona. It's just a matter of time."
Ronaldo has already netted 39 goals in 40 official appearances for Madrid so far this term.