Following his side's 2-0 derby loss to bitter rivals Borussia Dortmund on Saturday, the Dutch trainer has opined that the Spaniard has not regularly brought his best performances.
"He's played inconsistently this season, with good and bad moments," Stevens said according to Bild.
He added, however, that this is not entirely the fault of the veteran, who although deployed in midfield, is as much a striker as a playmaker.
"Our current midfield problem, however, Raul cannot solve. He is a striker, a nine and a half - he needs assists."
Stevens also claimed that Holtby has not matured as a leader in defensive midfield, and admitted that his side lack a spark in the absence of Jefferson Farfan.
"He's only 21, but he should be ahead of Julian Draxler, who is only 18. Lewis needs to be more present and to grow into the chief's role. Otherwise, without the injured Jefferson Farfan, we have no solutions. His quality has been missing in every nook and cranny."
Schalke have struggled since Farfan and captain Benedikt Howedes sustained knee injuries during the most recent international break. Looking ahead, Stevens believes his side can advance from Europa League Group J, and eagerly anticipates the return of Howedes, who resumed training this week.
"With a win we are through. And hopefully Benedikt Howedes will come back on Sunday against Augsburg."
Schalke currently top their Europa League group with eight points, two ahead of Maccabi Haifa. Their Bundesliga campaign has been slightly less fruitful thus far, leading to a fifth-placed standing after 14 games.
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