Porto goalkeeper Iker Casillas insisted Chelsea remain a force to be reckoned with in Europe, despite the English champions' domestic woes.
Chelsea slumped to their eighth Premier League defeat on Saturday, surprisingly beaten 1-0 at home to AFC Bournemouth.
Jose Mourinho's Chelsea languish in 14th position, 14 points adrift of Manchester United, who occupy the fourth and final Champions League spot.
While Chelsea's Premier League struggles are evident, the Londoners remain on track to qualify for the Champions League knockout round heading into Wednesday's Group G showdown with Porto.
Chelsea top the group ahead of the Portuguese giants on goal difference, while Dynamo Kiev are two points adrift and Casillas has warned his team-mates not to underestimate Mourinho and Co.
"Mourinho is a coach who will always want a victory and now against his old club," Casillas said.
"But we fly with the mentality that we can make them suffer at Stamford Bridge and get through the group phase. To be out of the Champions League in the next few days would be a big blow.
"Chelsea are not playing with the same level that they played in the past seasons but the Blues have an enormous squad that is capable of beating any European rival.
"It's never easy to play English clubs in their own stadiums with the atmosphere there. But this match is decisive for us. After failing in the last match it’s now obligatory that we go to London and show our best side and, as a minimum, take one point on the pitch.
"Porto has not prepared for a defensive match because that will be a disaster and almost certainly result in a defeat. We are obsessed with staying in the Champions League.
"We have had a good group phase but the pain was the defeat at home by Dinamo Kyiv. That was our worst match of the season and we have to be confident that that will not damage our European chances."
