Otero also acknowledged that talking with Birmingham remains the priority and Zarate has confirmed he is keen to stay with Alex McLeish's side.
With Al-Sadd's demands potentially out of Blues' reach, Otero admits another loan agreement is one option which could be discussed.
"The Qataris want more than they paid for him, but another loan deal might be possible," Otero told the Daily Mirror.
"It is not easy, but Birmingham have priority as they have given Mauro a chance and he is comfortable with the manager Alex McLeish.
"Mauro has captured the attention of other clubs as people can see he will be a top, top player."