The 31-year-old midfielder limped out of last weekend's 2-2 draw against Tottenham Hotspur after another fine big-game display came to an abrupt end -- the latest setback in a career increasingly blighted by fitness problems.
Kante remains a vital part of Tuchel's squad but he started just 21 Premier League matches last season amid persistent knee and groin injuries, while he also contracted COVID-19.
And when asked for the latest on the France international's availability, Tuchel said: "[It is] quite serious. We are talking about weeks. Not good news. We are disappointed and sad because N'Golo was super important and super fit. He will be out for several weeks."
Chelsea will also be without striker Armando Broja and Mateo Kovacic against Leeds, while Tuchel is awaiting the outcome of an English Football Association inquiry to determine whether he will face a touchline ban after receiving a red card after the final whistle against Spurs.
Tuchel and his opposite number Antonio Conte were also both charged by the FA with improper behaviour after clashing twice and the Chelsea boss is being investigated for comments he made regarding referee Anthony Taylor.
Mike Dean, the Video Assistant Referee (VAR) for last Sunday's game against Tottenham, has subsequently admitted that he should have asked Taylor to review Cristian Romero's hair-pull on Marc Cucurella immediately before the corner which led to Spurs' stoppage-time equaliser.
"I've since studied the footage, spoken to other referees and, upon reflection, I should have asked Taylor to visit his pitchside monitor to take a look for himself," Dean said in a column for The Mail+.
In response, Tuchel said: "Hopefully I'm not too honest but if the mistake is that big and that obvious, what's the point of not admitting if the whole world sees it?
"I struggle a little bit to be fully impressed by the statement, I have to say. It is so clear and obvious, I still cannot understand how a referee cannot make a decision that was the right one."
Tuchel's bust-up with Conte led to players and staff getting involved twice, most significantly at the full-time whistle as a handshake between the two managers quickly escalated into an argument.
"It is very important to laugh about ourselves," Tuchel said.
"Of course we laugh [about the handshake turning into an internet meme]. I was laughing in the dressing room because it was the heat of the match and it was for me still not that bad, it was a handshake, a bit too long and too heavy handshake I admit it, but no harm was done, at least from my side.
"He spoke Italian to me so I never know how we didn't insult each other. The thing would have ended if there were not 20 people around us to make it look much worse than it actually was. But if you have [a] reaction like this, you need to live with the reaction towards it."