Chelsea goalkeeper Petr Cech has given under-fire Blues manager Andre Villas-Boas his backing, insisting "the players are to blame."With just two wins in their last seven matches in all competitions, the Portuguese coach has had to withstand the pressure that comes with a difficult patch of form at Stamford Bridge, but Cech admitted there is only so much his boss can be responsible for."The manager is not on the pitch, we are on the pitch and we are making mistakes," the keeper told the club's official website."He cannot do anything about individual mistakes while he is standing by the bench. So the players are to blame and we know it - and we try to make things happen and change."It is not easy but we keep going."During a difficult spell those individual mistakes tend to get punished, Cech added, urging his team-mates to pay more attention to detail."We can't really wonder how we lost because we didn't kill the game off and we repeated the same mistakes," he said."We have been talking recently about the same mistakes - concentration and little details when we don't go to clear the ball."I think we need to be much more aggressive in terms of defending and we get punished all the time."The 29-year old also refused to lay blame at the feet of the referee, who waved play on when it appeared that Didier Drogba had been fouled in the penalty area in the second half."There are no excuses," he said. "We need to look first at ourselves and then we can criticise the other people because we put ourselves in the situation where we were 1-0 up and we could have killed the game off."Then there would be no discussion whatsoever about things that were happening in the game. We have to take it like that and make sure that this is the last time it happens."Cech did not want to dwell on the errors of the match in Germany and credited Manuel Friedrich's winning header before insisting the squad's determination ahead of the Blues' crunch clash against Valencia."It [the header] was too good. I tried to reach it but I couldn't and that was the reason why the goal went in," he said."We have put ourselves in a difficult situation because we could have had qualification done a month ago but that is the way it is. We play at home and it is up to us to deal with the situation."We are one of the top teams in Europe and this is not a situation we want to be in. The reaction of the players is that we can show on the pitch that we really mean what we say."