James has completed just one full match so far in Russia, however, having carried a calf injury into the tournament that has plagued him throughout the group phase.
Pekerman now fears being without James in four days' time for the crunch clash with England.
"I am extremely concerned. It's a tough situation for my team and a topic that could overshadow everything else," he told reporters. "It's not a comfortable situation for us. He trained normally yesterday, he was fully fit, no hint of injury.
"But right now I don't know where he stands to be honest. Hopefully there will be good news after he has been for his medical examination."
James has had a hand in 10 goals in eight World Cup appearances, scoring six and setting up four more.