The Dutch striker was injured in an international friendly against Germany in Amsterdam last week, pulling a thigh muscle.
"Afellay will in all likelihood miss training and he is also unlikely to play," Schalke 04 coach Huub Stevens told reporters on Tuesday. "It would be too dangerous to play him."
"Metzelder and Uchida are still building up intensity in training and it would be a risk to play them at this point," Stevens said. "We still have to decide about that."
Schalke's back-line looked out of sorts in their 2-0 defeat to Bayer Leverkusen on Saturday.
"We have written off the Leverkusen game and the only thing we are focusing now is to get to the next round," said Stevens.
"We accept the criticism for our performance against Leverkusen but what is more important is the entire picture after 34 league matches."
