The Bayern captain has missed the club's last two matches with a hand injury.
"The last decision is always with the player," Kovac told reporters. "We talked together [before the Hertha game] and he said: not yet. And probably not for tomorrow's game.
"We'll wait and see how it develops and we will not use him until Manuel says he is okay.
"I cannot say exactly how it [the injury] happened, we had a very intensive goalkeeper training.
"Our doctors, our staff and [club doctor] Hans-Wilhelm Muller-Wohlfahrt take care of him."