Palace went 1-0 up thanks to a Jean-Philippe Mateta penalty but as the game went on, were visibly tired having played in the Europa Conference League in midweek.
Man United bagged two second half goals to secure a much-needed win, taking Ruben Amorim’s side up to seventh.
After the game, Glasner once again vented his frustration towards the Palace board for their lack of investment in the summer window.
Glasner told BBC Match of the Day: "If you play European football for the first time in your history, you should invest and not save.
“We are doing well, we are still in a good position in the league and in all four competitions. I think January is too late. We will have played more than 50% of our games.
"Ismaila (Sarr) we lost him today with an injury and also he goes to AFCON so everything we are facing now, it's not surprising.
“Everything was pretty clear and I didn't say anything but today I think it is also time to speak about it that we missed the chance to play an even better season in the summer."
The Austrian's current contract at Crystal Palace is set to expire at the end of the season and he has been linked with several top Premier League clubs.