Frank Lampard has "no doubt" Timo Werner will come through his difficult spell of form for Chelsea.
Chelsea are under pressure ahead of Monday's home fixture with West Ham having lost two straight Premier League games, going down to both Everton and Wolves on the road. A third consecutive top-flight defeat would represent their worst run for over five years.
Germany international Werner, a high-profile signing from RB Leipzig, has not scored for eight matches across all competitions.
He particularly struggled to make an impact in the games against Everton and Wolves, but Lampard insists his deployment on the left of a front three is not the reason for his woes.
Asked why Werner was playing on the left, Chelsea boss Lampard said: "For different reasons. We had a big reference for a target man [Olivier Giroud].
"Timo for Leipzig and Germany played in lots of roles, so it is not a problem for him to be used there. He can be used across the front three.
"I have players who can play on both sides. Not all, like Hakim [Ziyech] on the right, but Timo and Christian [Pulisic] can play left and right. It can give the opposition a problem. I like to have the option to change it at times.
"With Timo, any goalscorer wants to score regularly but must have the mental toughness and confidence to go through periods. That is every striker. It is no problem. He needs to keep getting in those areas and the goals will come, no doubt."
Lampard says it would have been really beneficial for player welfare if five subs had been approved, but he recognises the decision has been made and we must carry on as we were. #CHEWHU— Chelsea FC (@ChelseaFC) December 18, 2020
Late checks will be made on the fitness of wingers Ziyech and Callum Hudson-Odoi, who both trained on Friday after spells out with injury.
West Ham did the double over Chelsea last season, winning the match at Stamford Bridge 1-0. That was the first time in 14 attempts they had won away at Chelsea in the Premier League.
Declan Rice continues to impress for West Ham and England, leading to Lampard being asked if he regretted Chelsea allowing the youth product to slip through their fingers.
On West Ham, Lampard acknowledges the good work done by David Moyes this season and says they are well coached in many different areas. He says as a player the fixture meant more to him, but now as a manager it is just another game. #CHEWHU— Chelsea FC (@ChelseaFC) December 18, 2020
"He is a fantastic player for West Ham and England - fair play," Lampard said about Rice. "It's a good story because with a lot of those stories, it shows a strength of character.
"I wouldn't say it's a regret. Our academy is one of the best in the world and it's not easy because it's not an exact science. Declan deserves personal credit for the start he has had at West Ham."
Three straight wins against the Blues would be West Ham's best run in the fixture for 46 years. It is the start of a key stretch for Chelsea, with matches against Arsenal, Aston Villa and Manchester City also coming up during the busy festive period.