Chelsea goalkeeper Petr Cech reckons Arsenal will be out of the title race if they lose to the Premier League leaders at Stamford Bridge on Sunday.
Arsenal have lost five league matches already this season, have slipped 10 points behind pacesetters Chelsea and Liverpool and are currently not even in the top four.
"For them it is a must not lose game," Cech told Chelsea's website. "If they lose they are out of the title race completely."
Arsenal coach Arsene Wenger believes the London derby offers a chance for his side to kickstart their title challenge.
"Ideally, I do not want to be 13 points behind Chelsea so let's make it seven on Sunday night," he said. "We know that direct confrontations with top teams become vital when you are in our position."
Champions Manchester United are also in action, knowing they can ill afford any slips at local rivals Manchester City. United, eight points behind Chelsea and Liverpool with a game in hand, were beaten home and away by City last season.
Tottenham Hotspur's resurgence under new manager Harry Redknapp will be tested when they host mid-table Everton at White Hart Lane looking to move clear of the relegation zone.