Chelsea's 1-0 defeat by Marseille in their final Champions League Group F game, courtesy of an 81st-minute winner from Brandao, left the Blues with just two wins out of the last eight in all competitions.
It also left coach Carlo Ancelotti in a dark mood as Chelsea now embark on a period of matches that could define their season.
Enough is enough: Terry (left) is determined to return to winning ways
Terry said: 'There is no point us panicking. We realise we are not playing as well as we can, the players realise there is a lot more to give and to come.'
Chelsea face fixtures against Tottenham, Manchester United and Arsenal but Terry added: 'Sunday is a massive derby for us and for the fans. We're hoping to kick-start an important time for us.'
Testing times: Blues boss Ancelotti
Ancelotti looked defeated, dejected and dismayed by the latest setback but vowed he had the strength to get through the tough times.
'We had an opportunity to move on out of this period,' said Ancelotti. 'We lost this opportunity because we didn't win and we didn't play so well. I'm not low; I'm strong.
'I want to resolve this problem quickly. I'm focused on my job. This is normal. I think my players have that same focus. I'm sure of this.
'But we have to keep going and look forward. We have a great opportunity against Tottenham, a difficult game away against a top team.
'We must consider that a good opportunity. Now everyone thinks we will lose that game. For this, we need to prepare that game well and try to win it.
'We have to consider this a great opportunity for us. Not a problem. We don't have to lose composure, character, our ability. We have to maintain confidence for the future.'
Ancelotti was given more bad news when it transpired that right-back Jose Bosingwa, only just back after a lengthy absence with a knee injury, is out of Sunday's game against Spurs with a hamstring problem.
He is also pinning his hopes on a return to action for England midfielder Frank Lampard.
Crocked: Defender Bosingwa (left) suffered a hamstring injury against Marseille
'Bosingwa has a hamstring, so he's not available for the next game. Frank trained today and had a good session,' said Ancelotti. 'We'll take a decision in the next two days. He'll train with us.'
But Chelsea looked like a pale shadow of the double-winning side of last year.
They could easily have been two goals down by the break but Gabriel Heinze's effort was ruled offside and the crossbar intervened when Mathieu Valbuena's 20-yard shot had beaten Petr Cech.
Chelsea had two penalty appeals turned down and both looked genuine. Indeed, the Blues appeared to have been given a penalty by Russian referee Vladislav Bezborodov when Souleymane Diawara brought down Florent Malouda.
The official pointed to the spot but, under pressure from Marseille players, appeared to consult his linesman and change his mind.
'He gave a penalty then said Florent dived - but if that's the case you have to give him a yellow card,' said Chelsea striker Didier Drogba. 'It changed the game - 1-0 for us would have made it a different game.'
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