Bale, 26, limped out of Real's 4-0 Champions League win over Shakhtar Donetsk in midweek.
But Benitez expects the former Spurs player to be fit for his country's Euro 2016 qualifiers against Bosnia-Herzegovina and Andorra next month.
"It is a small injury and it appears he recovers quickly," said Benitez.
Bale has scored six of Wales' nine goals in Euro 2016 qualifying.
Benitez believes he should be available for their two fixtures in October, which they enter needing a point to qualify for their first major tournament since the 1958 World Cup.
"We are optimistic," he said.
"If the player is fit to go with the national team there is little you can do apart from the normal conversations with the national team managers.
"The most important thing is that Gareth recovers as quickly as possible."
Wales forward Gareth Bale is set to be out "for two to three weeks" with a calf injury, according to Real Madrid manager Rafael Benitez.