The 21-year-old has attracted the attention of several European clubs in recent months and has most notably been linked with Premier League side Crystal Palace.
Cameroon-born Ntep has scored three goals in Auxerre's opening 12 Ligue 2 fixtures and has made an immediate impact in the France Under 21 side.
The forward has scored four in four for Willy Sagnol's team as they pursue qualification for the 2015 UEFA Under 21 Championship in the Czech Republic.
However, Auxerre appear determined to hold on to the frontman as Cotret insisted it will take a substantial bid for the club to release Ntep.
"His possible departure will depend on the offer, which should be huge, but there is nothing concrete so far, but it will also depend on our situation in January," he told L'Equipe.
"We won't let him leave if we are in competition to get promotion to Le Championnat."
Ntep is currently contracted with Auxerre, who sit 14th in the French second tier, until 2015.