Manuel Pellegrini wants his West Ham side to show they can play "exactly the same way" as Manchester United when the teams meet at the London Stadium on Sunday.
Last season, West Ham ran out 3-1 winners in the fixture, as goals from Felipe Anderson and Marko Arnautovic and an own goal from Victor Lindelof sealed all three points for the Hammers.
United have had a congested fixture list and their clash with West Ham will be their third match in just nine days.
On whether it was a good time to play United given the number of matches they have played, Pellegrini said: "They played yesterday night (on Thursday against Astana) but they changed nine players so it will be absolutely a different team.
"More than when is the best time to play against United, I think we are in a good moment so if we need to play against these big teams now we must demonstrate that we are able to play exactly the same way they do."
The Chilean added: "We know that we have a very strong team in front of us, now we have a good test against United and we will try to beat them and it's the only way to try to arrive in the first six positions of the table, demonstrating every game that you are able to do it."
The Hammers go into the game level on points with United, and are unbeaten in their last five matches in all competitions.
When asked about his side's defensive strength, Pellegrini said: "We defend as a team, that is very important.
"At this moment we are doing well and that is why we have the results and clean sheets but we must continue to not make mistakes."
West Ham will be without Winston Reid, who is still recovering from his long-term knee injury, but he could return for the under-23s next week or the week after.
Manuel Lanzini has a small problem, which will be assessed on Saturday, but all other players remain available to Pellegrini.
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