Pellegrini enjoyed a strong start to his second season at the London Stadium as West Ham won three of their opening six league matches.

But the former Manchester City boss, 66, has overseen just one victory in the Hammers' last 11 matches, with the club facing the distinct possibility of a relegation scrap unless results dramatically improve.

Angelo Ogbonna gave the hosts a 1-0 interval lead on Monday evening only for the Gunners to score three times in nine second-half minutes to condemn Pellegrini to his latest loss.

Pellegrini was roundly booed by the disgruntled home fans for his decision to replace Felipe Anderson with Sebastian Haller moments after Pierre-Emerick Aubameyang scored the visitors' third.

But the Brazilian, who has failed to find the net this season despite starting 15 of West Ham's 16 league appearances, says it is down to him to recapture his form.

"This is the worst phase I have been going through with the team," said Anderson, who scored nine goals in his debut campaign with West Ham last season after signing from Lazio.

"When I arrived it was hard but we started winning and I started to show my potential by helping the team with goals, assists and dribbles, and right now things are not working out as we want.

"Things have to improve and I have to improve to be able to help the team.

"As I always say, this is a collective game. If I don't score and the team wins, I'm happy, but if I don't score and the team loses and I couldn't help the team as I want to, it's difficult but we need to keep on working hard and think positively.

"Monday's match was a very negative result and one that we didn't expect because we were at home and because we had played well in the previous two matches, but we know that we need to keep working hard to get out of this situation."

West Ham travel to St Mary's Stadium on Saturday. They then head to Crystal Palace on Boxing Day before seeing out the year with a home match against high-flying Leicester.