The London club lost for the third time in five games on Wednesday, going down 2-1 at Bayer Leverkusen in the Champions League.
Portuguese Villas-Boas, 34, took over when the experienced Carlo Ancelotti was sacked in the close season but his tactics and team selections are starting to come in for widespread criticism.
"The manager is not on the pitch, we are on the pitch and we are making mistakes," Cech told the club's website on Thursday. "He cannot do anything about individual mistakes while he is standing by the bench.
"The players are to blame and we know it. There are no excuses."
The defeat at Leverkusen means Villas-Boas's men need a victory or a goalless draw against the Spaniards in their final Group E game to seal a place in the first knockout round. Leverkusen are already through.
"We can't really wonder how we lost because we didn't kill the game off and we repeated the same mistakes," said Cech. "We have been talking recently about the same mistakes - concentration and little details when we don't clear the ball.
"I think we need to be much more aggressive in terms of defending... we have to make sure this is the last time it happens."
The Czech goalkeeper has been blamed in some quarters for Leverkusen's late winner but he said Friedrich's header was simply unstoppable as the ball dipped just under the bar.
"It was too good," said Cech. "I tried to reach it but I couldn't and that was the reason the goal went in.
"We have put ourselves in a difficult situation... but that is the way it is. We are one of the top teams in Europe and this is not a situation we want to be in."
