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West Ham are enjoying a brilliant run of form in the Premier League, but if Sebastien Haller is missing for an extended period of time their ambitions this season could take a serious knock.

Since an opening day defeat against Manchester City the Hammers have gone six unbeaten in the league, scored goals, and now sit fifth in the table.

Andriy Yarmolenko has hit a rich vein of form and popped up with three goals in six league games, but Haller is the man who ties the attack together, acting as a focal point to link-up play with the creative midfielders playing just behind him.

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The £45m man has averaged 1.2 key passes per game in the Premier League, which underlines how adept he is at creating openings for his teammates to flourish.

It is little surprise, therefore, that Yarmolenko has burst into life.

Haller has been similarly effective in front of goal, also scoring three times in six games like his teammate and using his head well to score against Watford, an asset of his game which makes him central to the way West Ham play.

He uses his large frame to his advantage often, averaging 7.2 aerial duels won per game, which also allows his hold-up play to be effective, an aspect of his game which isn't shared by fellow summer recruit Albian Ajeti.

Against Oxford the Switzerland international got his chance to impress but instead displayed that he is not up to the task of leading the West Ham line on his own.

In his defence, he is young and still adjusting to a new league, but it will be a worry for Manuel Pellegrini if he has to rely on the former Basel striker as a back-up for Haller, even if just for a temporary basis.

That is partly because the 25-year-old has averaged 34 passes per game so far, more than any other striker in the Premier League, and therefore he is a big influence in every Hammers game and missing that focal point - as they did against Oxford - will disrupt their flow.

His absence could even cause Pellegrini to adjust his formation or experiment with Michail Antonio or Yarmolenko up front, and they would likely find it very difficult to maintain their current position if that happened.