Nkunku, a summer signing who suffered a knee injury in preseason, was only able to come off the bench in the Carabao Cup final loss to Liverpool, and seemingly injured himself in the game.
Pochettino said: "Yes, that is a good point. After 90 minutes, I think we were the better side because I think you can talk for many reasons; tactics or different things. But the energy is the most important thing to try and keep. When we started extra-time, Gallagher and Chilwell were not available for different reasons.
"Another player like Malo Gusto, Levi Colwill or Disasi, or even Moises Caicedo or Enzo, they were tired and we didn't have from the bench because Lavia is injured, Lesley is injured, Carney. There is too many players we didn't have in this moment to help the team, to put some energy in the middle, to keep pushing.
"You make the reference to Nkunku, yes it is difficult for him. We were watching, because it is our job, when he arrived in the pre-season, he was flying on the pitch, in training in America, until he got the knee injury. And now it is nearly eight months, even when he was ready to be involved again, he was never the same player as he was before.
"We have in our head, the potential, the best Nkunku that everyone knows from Germany, the Bundesliga, that is not the same player when we needed an impact, like in the final because of different circumstances. That is why it is unfair to judge, the situation is different but we need to respect opinions.
"Yes, for the team, it is not a good thing for us. We cannot provide to the team a player that can perform, score goals and be important in this type of game."
He then added: "Ah, sorry the question was sorry, sorry, sorry (laughs). We need to see. At the moment it is three or four weeks maybe out. (We) hope three or four weeks, no more."