Hummels was one of a number of players to criticise Germany's tactics after a 1-0 loss to Mexico in their Group F opener.
The Bayern Munich man later said talks in Germany's training camp had cleared the air ahead of facing Sweden in Sochi.
The centre-back is struggling with a neck complaint and is unavailable for the second game, according to Low.
"Hummels won't be able to play tomorrow. He hurt his neck [vertebrae] yesterday and he hasn't improved today," he told a news conference.
"He cannot train but there's still some time. When things like that happen, it doesn't improve overnight.
"We need players good in aerial play. I have an idea, a match plan for tomorrow. We will see what the final session yields."
Still having some hope for tomorrow, you simply don’t want to have to watch such an important game...— Mats Hummels (@matshummels) June 22, 2018
But just as Hummels defied his coach in the wake of their defeat, he contradicted him again when he tweeted: "Still having some hope for tomorrow, you simply don’t want to have to watch such an important game."
Germany could be knocked out if they lose to Sweden depending on Mexico's result in their second pool match against South Korea.