Huntelaar out of Valencia clash
Huntelaar, who has not scored this year in any competition, has injured his knee ligaments and missed his team's last two Bundesliga games.
"He is making progress but is not yet fit enough to play," Magath told reporters.
Schalke will have to rely on Spanish striker Raul, who scored in the 1-1 draw at Valencia.
"It would be far too dangerous to sit back and play for a goalless draw," Magath told reporters. "One careless moment towards the end and it could all be lost," the 57-year-old added.
Raul has scored a record 69 goals in the Champions League, mainly for his former club Real Madrid.
"I expect Valencia to be even more dangerous than in the first leg," the 33-year-old said. "We have a small advantage but they have the quality to turn this tie around."