Both strikers have been most often used in turn and between them, Benzema and Higuain have scored just 13 Liga goals.
The former Merengues coach suggests the players' poor form is down to the uncertainty created by Mourinho's rotation policy up front.
“I think their duel for the one position has been of benefit for a while. But there comes a time that when you are having to prove yourself every day that you begin to tire," Valdano told Cadena SER.
“Neither has won the race. Some weeks we see a step forward for Higuain, other weeks Benzema looks to be ahead.
“If we look at the statistics, the two are getting fewer goals than last season.
“But I encourage them to decide, not even the fans know who is starting each game. And that uncertainty is often uncomfortable for the big stars.
“Especially so if the situation is prolonged for a long time. It doesn’t help Real Madrid for their game nor their aggressiveness, which they had last season.”
Valdano then criticised the number of games professional footballers are expected to play.
“It is increasingly difficult to work around a calendar that is this crazy," he continued.
"The players today are true heroes, because they travel around the world, sleep on planes and when short on fitness go out on the field, whilst we require that they also live like monks.
“A footballer today runs 11 or 12 miles a game. Twenty years ago you ran eight per game and then you might play three times one week and twice the next, but now they play every Wednesday and every Sunday.”