Juanma, who's contract at the La Liga club expires this summer, is said to be considering Blues' offer has he prefers to stay in Spain.
"The English offer is excellent in the money question, but the player has decided to wait a little while before giving an answer," Juanma's agent Mario Parri has told skysports.com.
"Birmingham desire to be a good team in the Premiership and the project is interesting in all aspects."