Defender Schmelzer will need to wear a facemask after breaking his nose in the league on Saturday, while midfielder Blaszczykowski is nursing a groin injury.
"It is up the medical staff to have the final word," said Zorc prior to the team's departure. Dortmund have yet to lose a game in the tournament this season.
The 1997 Champions League winners, who host the Spaniards in the return leg later this month, are looking for their first semi-final appearance in 15 years.
"That time gap alone reveals how important this game is for us. We want to continue having fun on the pitch," Zorc told reporters.