Manager John Ward said Colchester United's performance in the Johnstone's Paint Trophy on Tuesday was 'not acceptable.'
The U's lost 3-1 at home to League Two Barnet in the first round to fall at the first hurdle for the third year running.
Ward told BBC Essex: "I have to say that's not acceptable, and we've got to immediately get that back on par.
"If we play like that on Saturday, Scunthorpe will beat us as well."
The U's handed first starts of the season to Ben Williams, Pat Baldwin, Andy Bond and Steven Gillespie but were dumped out despite playing against ten men for the last 25 minutes.