West Ham United co-owner David Sullivan has admitted that the board are "struggling to understand" the club's downturn in form this season.

After a seventh-place finish last term, the Hammers are currently 13th in the Premier League and have lost 10 of their 20 games so far.

Slaven Bilic's side are currently on a run of three straight defeats in all competitions, with back-to-back league losses to Leicester City and Manchester United compounded by a 5-0 hammering at home to Manchester City in the FA Cup last Friday.

"We haven't lost any key or influential players since last season, which was one to remember, so we are all currently struggling to understand why the team is under-performing at this moment in time," Sullivan wrote in a post on the club's website.

"We know we have to improve quickly, and upcoming fixtures against Crystal Palace and Middlesbrough now become cup finals. As we showed over Christmas, though, a string of good results can move you up the Premier League table very quickly, and I am confident we will be heading in that direction over the coming weeks.

"I know it can be difficult at times like this, but I urge every supporter to get behind the team and manager – just as you have done all season. We have seen performances improve recently, even in defeat at Leicester City and against Manchester United, so I truly believe we can continue to progress if we all push in the same direction."

West Ham next welcome former manager Sam Allardyce's Crystal Palace side to the London Stadium on Saturday afternoon.