France striker Benzema missed the visit of Borussia Dortmund in the Champions League on Tuesday with a thigh muscle problem and Argentina's Higuain was forced out at half-time in the same match with what looked like a hamstring injury.
"I don't think Benzema or Higuain will be available this weekend," Mourinho said after the 2-2 draw at the Bernabeu.
Jose Callejon came on and deputised up front in the second half on Tuesday, while youth team striker Alvaro Morata could get a call up to the first team.
Portugal left-back Fabio Coentrao returned to training with the squad on Thursday after picking an injury on the last break for internationals.
The champions trail leaders Barcelona by eight points after 10 games and visit the Ciudad de Valencia stadium on Sunday, where they lost one of only two league games during the whole of last season.
Levante, who lie sixth in the standings three points behind Real in third, upset the visitors 1-0 in September last year when Sami Khedira was sent off and Arouna Kone scored the game's only goal.
Two years ago, newly-promoted Levante held Real to a 0-0 draw there and also surprised Mourinho's men 2-0 in a King's Cup last-16 first leg, though they ended up losing 8-2 on aggregate.
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