Nkunku has not yet played competitively for the club after injuring his knee on their pre-season US tour, weeks after joining from RB Leipzig for £52 million.
The Frenchman, last season's Bundesliga top scorer, was named in Pochettino's squad for Saturday's 2-0 win against Sheffield United as the team registered back-to-back Premier League home wins for the first time in more than a year.
He did not feature but is set to make his competitive debut on Tuesday for Pochettino's side, who struggled to break down their opponents at the weekend.
"I can tell you maybe he can play 20 minutes," the Chelsea boss said at his pre-match press conference on Monday.
"How I saw him before Saturday in my mind I had one per cent to two per cent of doubt. That's why I didn't want to take a risk.
"I need to be 100 per cent, then things can happen."
Chelsea have scored 28 goals in 17 league games this campaign, but they have come in bursts, with the team, 10th in the Premier League, failing to net at all in the league during September.
Pochettino urged supporters to show patience with their new forward, who scored 16 goals for Leipzig last season.
"(Nkunku has trained) only in the last few weeks, after four or five months he was out," said the Argentine. "The team has evolved and the situation has changed.
"My worry is to put too much pressure on him, to say 'now has arrived the guy to make us win every single game, to change everything'. I don't believe it's going to be like that.
"He needs time to recover his fitness. Hopefully, he'll play tomorrow and score three goals, then be consistent. But the most important thing is not to put too much pressure on him."
Nicolas Jackson is the top-scorer for Chelsea this season, with eight goals in all competitions, while the impressive Cole Palmer and Raheem Sterling each have six.
Newcastle boss Eddie Howe hopes his team can draw on the disappointment of losing last season's League Cup final against Manchester United.
"I'm just devastated we didn't get over the line in the end," he said.
"I think it's helped us for this year and we know this game's going to be very difficult but we know the prize if we can get through."
The Chelsea match at Stamford Bridge will mark Howe's 100th game in charge of Newcastle since he was appointed in November 2021.
"I've loved every second of it," he said. "When you look back at a group of games, so many highlights, memories."
