The 19-year-old prospect, who in just two years has become indispensable for both Schalke and Germany, picked up a heel injury and nasty cut to his calf in last week's 3-3 draw against Hamburg, and only returned to light training on Wednesday.
"Whether he will be fit in time for the Wolfsburg game remains unclear," the club said in a statement.
Schalke, who next week face Greece's PAOK for a spot in the Champions League group stage after Ukraine's Metalist Kharkiv were disqualified for match-fixing on Wednesday, will be hoping to avoid dropping too many points early this season.
Their campaign floundered early a year ago and they needed a late-season surge to finish fourth in the league and salvage a Champions League playoff berth.
"We obviously all know what we have with Julian," team mate Christian Clemens told reporters. "You can easily see that when he is not there, we lack a bit of creativity. We hope he will be fit in time for the game."
In last week's season opener, Schalke rallied twice to level against Hamburg and Clemens, who joined in the close season, said the two dropped points from that game needed to be recouped in Wolfsburg.
"It did not work out with a win against Hamburg, so we are even more motivated to win at Wolfsburg."
The 2009 Bundesliga champions, on the other hand, will be looking for their first points of the season after suffering a 2-0 defeat at regional rivals Hanover 96 last week.
They also want to strengthen their squad and are hoping to wrap up a deal for Bayern Munich midfielder Luiz Gustavo.
According to several German media sources, the deal with the Brazilian, who is desperate to play regularly ahead of next year's World Cup on home soil, was all but sealed.
Treble winners Bayern travel to Eintracht Frankfurt, who are still reeling from their 6-1 opening defeat to Hertha Berlin. Bayern looked to have lost none of their sharpness when they eased past Borussia Moenchengladbach 3-1 last week.
Last season's Bundesliga and Champions League runners-up Borussia Dortmund host promoted Eintracht Braunschweig on Sunday.
Dortmund playmaker Ilkay Guendogan is a doubt after he came off with a back injury in Germany's 3-3 draw with Paraguay on Wednesday, a game in which he scored the home side's first goal.