The Portuguese coach is sure his midfielder will not pick up a booking in order to ensure his availability for the Clasico because 'every match is important'
Alonso has picked up four domestic bookings this campaign, meaning another will result in a one-match ban.
Last season, Alonso and Sergio Ramos caused controversy - and were later hit with fines - after getting themselves sent off in the Champions League group stage against Ajax, ensuring a clean disciplinary record for the knockout phase of the tournament.
But speaking at the pre-match press conference ahead of his side's game against Atletico, Mourinho denied that Alonso would repeat the trick in the Madrid derby.
"He 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 technical area 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.
"I want Benzema and Higuain to keep this up until 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 to do so in an impressive manner.
"People who think the derby will be easy are wrong. I would settle for a 1-0 victory 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.
"Kaka won't play, but he'll 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."
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