The Portuguese coach is sure that the midfielder will not pick up a booking in order to ensure his availability for El Clasico and says every match is important
Alonso has picked up four domestic bookings this campaign, meaning just one more will result in an instant one-match ban.
Last season, Alonso and Sergio Ramos caused controversy by getting sent off in the Champions League group stage, ensuring they would have a clean disciplinary record for the knock-out phase of the tournament.
Speaking at his pre-match press conference, Mourinho denied that Alonso would repeat the trick in the Madrid derby.
He said: "Xabi Alonso is not going to force a booking tomorrow because every game is important to us and Real Madrid players are the only ones who aren't allowed to force a yellow card.
"Xabi is a very important player and that's why he plays most of the time. He feels strong and biological age isn't important in many cases.
"He gives the team balance. I've already told him that we'll meet in the bench areas again in the future since I intend to coach for another 30 years."
Meanwhile, the 48-year-old voiced his hope that his striking duo of Karim Benzema and Gonzalo Higuain can keep up their impressive form for the rest of the season.
Mourinho added: "I want Benzema and Higuain to keep this up till the end so that I continue to find it difficult to choose between them. They are both fantastic players in excellent form."
The former Chelsea and Inter boss then called upon his men to vanquish their local rivals and hopes to do so in an impressive manner.
"People who think the derby will be easy are wrong," he insisted.
"I would settle for a 1-0 victory if you offered me that today. My players are aware that anything can happen in every match. Our intention is to win, play well and produce a spectacle."
Finally, Mourinho confirmed that Kaka will be unable to return to the matchday squad, but expects the Brazilian to recover from his leg injury soon.
He concluded: "Kaka won't play, but he will return. He has an uncomfortable injury and feels minor pain still.
"He is doing field work and I think he will train with the rest of the team on Tuesday."