David Horseman said we must improve our levels after falling to a 5-1 defeat against Slavia Prague in the UEFA Youth League.
Two goals from set pieces and breakaway strike meant we were trailing 3-0 at half-time before Ceadach O'Neill pulled one back in the second half. But two late strikes means we are now without a point in our opening four Youth League contests.
Following the match, Horseman said we were not near our usual levels in the defeat in the Czech capital.
He said: "A really disappointing day for me and for the staff, because I think we put a lot of effort into this game and then more for the players because I don't think they showcased what Arsenal's all about, particularly in the academy.