Roberto De Zerbi admitted Albion’s efforts over 120 minutes in Sunday's FA Cup semi-final affected their performance in the 3-1 defeat to Nottingham Forest at the City Ground.
Facundo Buonanotte put Albion in front after Jason Steele saved an early penalty, but Forest equalised through Pascal Gross’ own goal before scoring twice in the second half to move out of the bottom three.
“We deserved to lose the game, congratulations to Nottingham,” said De Zerbi. “We played the first 30 minutes very well and we could have scored more goals.
“Then we lost energy, and the game. It was a possibility that we could lose energy and our speed. We played 120 minutes on Sunday - a very tough game a few days ago - and spent a lot of mental energy at Wembley. And today we suffered, especially in the second half.
“We are frustrated but I am always proud of my players. This is a very tough moment for us, we are playing a lot of games and have a lot of injuries, but I don’t want find excuses, I want to be honest.
“We are not used to playing every three days and we are missing some important players but we have to find the energy to play Wolves in our stadium on Saturday because we want to fight until the end of the season for a place in Europe.”