The 27-year-old will stay on loan at Nancy for the rest of the season.
“Given our offensive difficulties, the signing of Jung Jo-Gook is not an indulgence,” Fernandez told Eurosport.
“The fans surely would prefer that we sign a great player and I too, but it’s impossible financially.
“We are doing all we can, taking into account the urgency of the situation.
“Jo, as we called him at Auxerre, is a true striker who knows how to be opportunistic and has an excellent work ethic.”
