Palace were thumped 4-1 at Elland Road on the night, with Glasner not seeking excuses in the aftermath.
"It's like we were not sharp enough," he told his post-match press conference. "If you defend the set-plays like we did today, you have no chance to get a point in the Premier League.
"That's why at the end we lost and conceded all these goals. You have to win your duels. (Christantus) Uche did it at the end and all of a sudden we have a penalty.
"It's football, sometimes you can reduce it to the basics, and in the basics we were not good enough."
He added, "We will look in the mirror tomorrow. We will be, like always, very honest with ourselves. And I think there's a lot we have to talk about.
"Then we can show in three days that we can do better. Especially in set-pieces, when we're facing maybe the best set-piece team. That will be our job."