The Reds were beaten at the City Ground in the second round, with second-half goals from Daniel James and James Justin securing a 2-0 victory for the visitors.
Glasner admitted Forest’s performance was below the required standard but remains confident in his squad’s character.
“It was a tough night and a tough defeat. We have to accept it and it’s the reality of where we are right now,” he told media.
“They are further ahead of where we are. We have started our process but I think they have been together for two or three years now, always adding one or two or three players.
“This is what we could see, much more stability in the team, whereas we struggled today and we made too many mistakes.
“We knew we would play with pressure but we took too many wrong decisions and that’s how we gave them their chances and their goals.
“We had two or three moments where we had good opportunities but we didn’t take them but that’s the reality and that’s important for me to accept it.
“It’s we who can change it and this is what we will do.”