The Hammers were bested 5-0 at home, barely managing any shots on target in the contest.
While manager Julen Lopetegui was upbeat about their long-term outlook, he admitted this game was beyond them.
He stated: “I think that we played today against one of the best teams, very clearly, in the first half of the season.
“But despite this, I think that it has been a disappointing day for us because we are very disappointed for our fans above all. I think that we can lose this game, but I think that we can do better.
“It's true that there have been key moments when we had the possibility to draw the match (particularly when Kudus hit the post) but we didn't do it and they scored the second goal in the next action. It had been a strong moment for us and (after Kudus hit the post) I think that we didn't compete to meet the demands that this kind of team demand of you.
“So we have to learn, we have to look forward and to improve in many things to be able to stay closer in these kinds of matches.”