Los Blancos head into the crunch clash against their Catalan rivals four points clear at the top of the Liga standings, and Schuster believes it will be Pep Guardiola's side who will need to force the issue.
"Barca and Madrid reach this stage tired, which is normal," Schuster told COM Radio. "A draw will be good for Madrid, but victory would give them the league title.
"I do not see Mourinho trying to win, he will not take risks, he has never done that in matches like this. Losing the Liga like this would be disastrous."
Schuster, who stepped down as Madrid coach in 2008, says that the Portuguese coach enjoys special protection from the club's board - something that the other managers at the Santiago Bernabeu never had.
"Mourinho is the first Madrid coach who does not depend on results," he added.
"What he does in the press conferences delights me, because I would have liked to tell my assistant to speak in my stead, too.
"The way Madrid are organised and the power that Mourinho has at the club, I do not think that he will leave in the summer."
Questioned about whether Pep Guardiola will leave Barca at the end of the season, Schuster said: "I do not see any reason why he cannot continue.
"However, Guardiola's replacement must be a foreigner who carries the can.
"Then, there will be a new Spaniard."
Starting last month and continuing for 10 weeks, Goal.com is publishing exclusive extracts from Luca Caioli's new book, Ronaldo: The Obsession for Perfection. The fifth extract, published on Friday, looks at the Portuguese's intense rivalry with Barcelona's Lionel Messi ahead of this weekend's Clasico clash. Don't miss it!