The priest, Manuel Garcia Viejo, 69, was in serious condition and was suffering from dehydration, with kidney and liver complications, said Javier Rodriguez, chief health officer for the Madrid region.
Garcia Viejo, a medical director of the San Juan de Dios Hospital in Lunsar, Sierra Leone, was transferred to Madrid Carlos III hospital after being flown back from Sierra Leone in a medically-equipped military plane.
Mapp Biopharmaceutical, the company that makes ZMapp, says the drug's supplies are exhausted and that it takes months to make even a small batch.
With ZMapp unavailable, the hospital was looking into alternative medicines or the possibility of using blood serum from a cured patient, said Dr. Jose Ramon Arribas, of the Carlos III hospital.
Garcia Viejo is the second Spanish missionary to catch Ebola. Another priest, Miguel Pajares, 75, was flown back to Spain from Liberia on Aug. 7. Pajares began treatment with ZMapp, but died Aug. 12.
Ebola is blamed for the deaths of more than 2,600 people in West Africa.
The Health Ministry said Garcia Viejo asked to be transferred back to Spain after testing positive for the deadly virus.Suggest a correction