Nicolas Anelka is free to resume his career in England after completing an education course following his quenelle gesture.
St Mirren have signed winger James Dayton from Oldham on loan until the end of the season.
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.