The French attacking midfielder has been a substitute for most of the season in the Premier League this term.
While he has gotten game time in the Europa Conference League, there are suggestions he is unhappy at the club.
Maresca told reporters: "No, not at all. I spoke to Christo days ago and he did not say he was unhappy. For sure, he would like to play minutes but like many players.
“We have so many games, especially in December. Against Leicester, Joao played, Enzo played and Benoit played. Since we started, for me, there are not two squads - the squad is only one. They can play Conference League or the Premier League and the proof was against Leicester."
Asked if Nkunku was not available for transfer or loan, he added: "Absolutely, yes (will not be sold).”
He then added: "The problem with Christo, not the problem but it's the same issue and the same thing we mention many times about Joao. If you play with Cole, you play with Joao, or Christo, or Noni, or Jadon - who is defending? Their skills and strength is not defending; it's to attack.
"We love them but also we need the balance. Last game, we tried with Cole and Joao together. Soon, we can try with Christo and Cole, Christo and Joao, for sure. The reason why is because we have so many games. I completely want Christo to stay with us; I don't have any idea to let him leave in January."
On the qualities he admires in Nkunku, he finished: "Probably the best moment from Christo with us was in pre-season. For me, he was playing in his position; as a No.10, between the striker and the line. Since we started, he is playing as a No.9 with us. Against City in the first Premier League game, he played as a winger, knowing this was not his best position.
"Christo's best position is between the lines as a No.10 but Cole is playing there. We are not going to play many games with Cole and Christo, or Cole and Joao. We played the other day but we need the balance. The Leicester plan won't be the same as the Aston Villa plan. They are all fantastic players and are all going to play games, no doubt, but not every game."