Forest were 1-0 up on aggregate after the first leg against Aston Villa, but were blown away by Unai Emery’s side 4-0 in the second.
The Premier League strugglers were without six players due to injury, and although Morgan Gibbs-White was named on the bench, his bloody injury sustained in the win over Chelsea essentially ruled him out.
Speaking to TNT Sports after the game, Pereira believes that if he had his full squad at his disposal, the story could have been different.
"To compete in a semi-final and against a team like Aston Villa, we need everyone in the conditions to compete,” he said.
“If you look before the game on the bench we had three players, because the other ones were injured. Our bench today the only solutions we had from the first team was Bakwa, Luca, Murillo.
"We tried but he was injured and not in condition, and Yates. This is very short to come here without solutions.
"Playing against Chelsea and then travelling again to come here after three days, it was not possible. I'm very proud of our supporters, they tried on this long road to help us, but it was not possible. It is a pity but I am proud of my players because they tried everything."
When asked about why his side were unable to match Villa’s intensity, Pereira doubled down.
"Aina, out. Morgan (Gibbs-White) out. Sangare, out. Murillo, out. Callum (Hudson-Odoi), out. Ndoye, out. To bring the full squad we put three injured players on the bench, and we brought three more players from the academy," he added.
“To compete in a game in these conditions, after a game against Chelsea, and play in a semi-final is not possible. This is why I said we were not able to compete."