The BVB coach insists that his star man will not be rushed back to fitness after he picked up a muscle injury in last week's 5-1 win over Werder Bremen
The Germany attacker was initially ruled out for two weeks after picking up a muscle problem during the win over Werder Bremen last Saturday.
"We will not take any risks," Klopp told reporters.
"But we do not want to stop anyone who feels fit. Who knows? Maybe it's a good time for torn muscle fibres. They heal more quickly in this weather."
However, while Reus and Sven Bender appear set to make speedy recoveries, Ilkay Gundogan remains out of action because of a back injury, with Klopp admitting that the 23-year-old still "needs time" to return to full fitness.
Dortmund beat Frankfurt 1-0 in the DFB-Pokal in midweek and the 46-year-old believes Saturday's Signal Iduna Park clash will be tight affair once more.
"It was a tight game," he explained. "If we want to win on Saturday, we need to be really good."
Finally, Klopp slammed the antics of Carlos Zambrano, who was locked in an intense personal battle with Robert Lewandowski throughout the Pokal quarter-final.
"I think Zambrano is an oustanding central defender but some things do not please me, which we have just mentioned. They shouldn't be allowed.
"In the dressing room after the match, I asked the players who had swapped shirts with Zambrano. No one answered."