Ward-Prowse told the club's website: It was embarrassing on our part.
We had a fantastic night on Thursday albeit we didn't get through (to the UEFA Europa League semi-finals) but we showed what a West Ham team should look like. We were on the front foot and aggressive.
You can talk about the way you play with the ball but I think out of possession we didn't show enough aggression and togetherness against Crystal Palace. I think that cost us.
There are quite a few reasons why (we conceded four goals in the first 31 minutes) but I don't think the excuse of playing on Thursday night is anything we can use.
If we want to be a top team and be contenders for a European place, you can't perform like that against one of the best teams in the world at the moment Bayer Leverkusen, and then come to Crystal Palace and perform in the way that we did."
He added: You can't allow any team in football to score goals as easily as we did, especially in the Premier League. It doesn't matter if you're playing a team at the bottom or the top of the table, they will punish you.
There is still a lot of football to play, and because this is the business end of the season we know every game is magnified in that way.
(Liverpool) is a fantastic game to bounce back in and hopefully, we can give the fans something to cheer about against them."