Hakim Zayech, Timo Werner and Thiago Silva work out before Chelsea bid to break into top four - in pictures

Manager Frank Lampard has praised Chelsea's success in shoring up their defence but believes his players must guard against complacency when they host Sheffield United in the Premier League on Saturday. Lampard's side leaked nine goals in their opening five league games but have since kept five straight clean sheets in all competitions, which included a goalless league draw at Manchester United and a 3-0 win over Rennes in the Champions League. Timo Werner, Thiago Silva, Edouard Mendy and Hakim Ziyech were among the Chelsea stars working out before a game in which a win could take them into the top four, and Lampard said: "There's always different parts to it. "Individuals have made good performances in that period. The collective is a reflection of that. "It's driven by the players, always will be. We must never relax. It's such an important part of the game." Lampard said Chelsea have found a fresh balance in the team with new signings Werner and Ziyech being among the goals in their last three victories. "There's a versatility in the way new players play," Lampard added. "We had a slight change in formation and the 4-3-3 worked well recently." Lampard confirmed winger Christian Pulisic remains unavailable for the game at Stamford Bridge due to a hamstring injury. Midfielder Kai Havertz is ruled out as he self-isolates after a positive Covid-19 result, while goalkeeper Kepa Arrizabalaga (shoulder) is available though the Spaniard is still feeling some pain, the manager added. Chelsea are seventh in the league with 12 points from seven games, while Sheffield United are bottom after a winless start.

Hakim Zayech, Timo Werner and Thiago Silva work out before Chelsea bid to break into top four - in pictures

Manager Frank Lampard praises new-found defensive steel ahead of Sheffield United challenge