Steve Cooper admitted Dean Henderson being ineligible for Nottingham Forest's EFL Cup semi-final tie against Manchester United "put a dampener" on Wednesday's quarter-final win against Wolves.
Henderson was the hero in a tense penalty shoot-out at the City Ground after Raul Jimenez cancelled out Willy Boly's opener in a 1-1 draw, denying Ruben Neves and Joe Hodge as Forest triumphed 4-3.
However, the on-loan goalkeeper will be unable to feature in the final four after Forest were drawn to face his parent club United, leaving Cooper frustrated.
Asked about Henderson's situation in his post-match press conference, Cooper said: "It is unfortunate. That has put a bit of a dampener on it."
Speaking to BBC Radio 5 Live, Cooper hailed the goalkeeper's performance, saying: "We felt ready [for the penalty shoot-out], we did plan and prepare for it with Dean and the outfield guys, but even with that, it was still a bit of the luck of the gods.
"Dean was fantastic in the 90 minutes in keeping the ball out of the net, and he carried that over to the shoot-out."
Cooper was not overly enthusiastic about Forest's performance, however, adding: "I'm chuffed for the supporters and players.
"The objective of the tie was to get through. I can't say I loved our performance, I shouldn't be too negative and I won't be, but we have to play a lot better than we did for large spells of the game."
Meanwhile, Wolves counterpart Julen Lopetegui was frustrated by Graham Scott's failure to award a penalty when Matheus Nunes appeared to be fouled by Emmanuel Dennis late on, with no VAR in place to overturn the decision.
"It was very clear. Matheus went to control the ball and he didn't allow him to do it. It is very clear, we have seen the image," he said.
"Maybe I will have to review my knowledge of the rules. Maybe they are different. We have to accept it. The referee is the one who has the power to say yes or no. They don't have VAR today, it was a pity for us."