Chelsea's Frank Lampard defends under-fire goalkeeper Kepa Arrizabalaga

Chelsea boss Frank Lampard said goalkeeper Kepa Arrizabalaga is the first to admit that there is room for improvement after making errors this season but he is satisfied with his work ethic.

Kepa saved a penalty in Wednesday`s 2-2 Champions League draw at Valencia but came under criticism for failing to stop the two goals, especially the equaliser when he seemed to pull out of a save when Daniel Wass shot from distance.

"Like everybody, we`re all trying to improve. Kepa is a professional and you can see it in his attitude every day," Lampard told reporters ahead of Saturday`s London derby against West Ham United in the Premier League.

"He`s a keeper that`s striving to be better, as he should do at his age and the status he has -- Chelsea`s number one, big price tag, Spain`s number one and competing with another great goalkeeper (David De Gea).

"He`ll want to get better all the time, and there have been a few incidents this season where he`ll be the first to say he can do better. That`s football at the top level, but I`m happy with him and with his work ethic."

Lampard will be up against his former boss Manuel Pellegrini, who he played under at Manchester City, and the former midfielder was aware that a win for Chelsea could prove to be the final nail in the coffin for the Chilean manager.

Arsenal parted ways with Unai Emery earlier on Friday and Pellegrini is also under scrutiny with West Ham 17th in the standings after going winless in seven matches, which includes five defeats.

"He`s a good manager, I worked under him, he`s a good man, I`ve got huge respect for him," Lampard said. "He`s working hard just like every manager in the Premier League. He`ll be working to turn it around for them, of course.

"We all know the ruthless nature of the game now. Every team, every group of fans, the owner, everybody wants their team to be successful at all times and to push and to push. It doesn`t always work that way."