Leicester City manager Sven-Goran Eriksson was unhappy with his side after their surprise 3-0 defeat at home to Millwall.
A hat-trick for Darius Henderson has seen the Foxes slump to 13th place in the Championship table, and the Swede admitted that his side's performance wasn't good enough.
"I am angry and frustrated and very disappointed," he said. "We never looked like scoring today.
"Our first-half performance was not good enough. We looked like a team who were very tired, flat and with no ideas. We were moving the ball around okay but we didn't really hurt them.
"Perhaps we were tired. We have had three games in seven days which doesn't leave us much time to recover. I hope it was tiredness because if it wasn't I will be very worried."
Leicester travel to high-flying West Ham United next Saturday.
