Birmingham have confirmed that goalkeeper Darren Randolph is leaving the club after turning down a new contract.
MK Dons have seen an initial bid for Brentford's Will Grigg turned down, according to Sky sources.
The Blanquillos finished rock bottom of the Primera Division - albeit just three points adrift of 17th-placed Celta de Vigo - with previous boss Manolo Jimenez paying the price for the setback earlier this week.
Zaragoza have turned to former Liverpool assistant Herrera, who has managed a host of Segunda Division sides in the past, to guide them back into into the top flight.
The 59-year-old has signed a two-year deal.