Costa confident Blues will improve
Diego Costa is optimistic of a swift about-turn in fortunes for Chelsea.
The Blues lost 2-1 at Jose Mourinho's former club Porto to slip to third place in Champions League Group G.
Costa played two games into a three-match domestic suspension, but even his return could not boost Chelsea enough to claim victory.
The Spain striker, who was banned for violent conduct for grappling with Arsenal's Laurent Koscielny, said: "To come out of this we need to be all together, and for everyone to give a little more.
"We are not playing well, this is not a good moment, but we have players to get out of this easily."
Costa completes his ban in Saturday's Premier League clash with Southampton, but it is difficult to know who will replace him as fellow strikers Loic Remy and Radamel Falcao were not selected to travel to Portugal.
Oscar also did not fly, while Eden Hazard and Nemanja Matic joined captain John Terry on the substitutes' bench.
Nevertheless, Costa felt Chelsea did enough to win at Porto, only to concede a "ridiculous" winner from a corner.
"We had the game under control," Costa added. "We knew it was going to be a physical game. We began well.
"Things changed when they scored, but we quickly equalised. In the second half the same thing happened - we were lacking concentration at key moments of the game."
Chelsea will be seeking just a third Premier League win from eight games this season when Saints visit this weekend. Mourinho maintains his side can progress in the Champions League as Group G winners, despite the Porto loss.
Mourinho said: "We finish the group with Porto at Stamford Bridge. We have now a double match against Dynamo (Kiev). Hard, hard group, but obviously I think we can qualify and more than qualify - I think we still can finish first."
The Blues are understood to be keen to sign former AC Milan goalkeeper Marco Amelia as experienced cover for Asmir Begovic.