The Lions were beaten at home by Middlesbrough on Saturday and followed that up with a 2-1 defeat at Reading on Tuesday night to slip eight points adrift of sixth spot.
"If we aspire to make an impact at this level we have to be on top of our game every time," said Jackett.
"Against Reading we were way below that in every department and were beaten by the better team.
"Physically and mentally we were not right and there are no excuses. We have to be better than that."
Source: PA
Source: PA