Hummels injured his right thigh in Germany's opening FIFA World Cup game on Monday - a 4-0 win over Portugal - and has not been able to train fully since.
But coach Low insists the towering centre back, who netted the country's second goal against Portugal, will be given every chance to play at the Estadio Governador Placido Aderaldo Castelo in Fortaleza.
"Mats Hummels was running in training yesterday but he isn't 100 per cent fit," Low told reporters.
"We'll have to wait for the final training. He'll do the whole warm up and then we'll decide if he will do the full training with the team. He had no tackles and sprints.
"I don't like to have to form a new defensive line. That would not be the best situation.
"If we need to, then we'll find a good solution. We've good players to replace him."
If Hummels fails to prove his fitness, Low says there are two possibilities in terms of replacing the Borussia Dortmund player: "First: Jerome Boateng will play a central defender and we have to replace a right wing defender.
"Second: Boateng stays on the right and (Matthias) Ginter or (Shkodran) Mustafi will play as a central defender."
Low also refused to be drawn into Kevin-Prince Boateng's pre-match comments, after the Ghanaian midfielder claimed Germany lacked leadership.
"We don't speak about this, the team doesn't speak about it, (Kevin-Prince) Boateng hasn't played from beginning in the first match," Low said.
"I think he will be in the starting line tomorrow. But we don't think too much about this.
"We know the strength of Boateng from the Bundesliga. Meeting each other (Sami Khedira and KP Boateng) in a personal challenge we don't see it as a subject of discussion."
