The England captain is expected to arrive in Munich later on Friday to finalise the deal expected to cost 100 million euros, a Bundesliga record.
"We are working with full pressure on this deal," Tuchel said. "We can confirm this but as we speak there is no agreement yet and if there is no agreement yet then the coach cannot talk about someone who is not their player.
"I understand there are a lot of ifs and whens. All options are open. The first is to have him as a player and at the moment he is not yet that.
"This is a big deal. We are trying to take the England captain away from the Premier League."
Tottenham manager Ange Postecoglou told reporters ahead of his side's Sunday Premier League match at Brentford that he expected the deal to be completed.
"I understand it has progressed to where it will happen. That's all the information I have at the moment. It looks like we'll move forward without Harry," he said.
The coach said could not say whether Kane would be able to play on Saturday when Bayern kick off their season with the German Super Cup against RB Leipzig.
"We just had the last training before an important game. I will not get involved in the final hours of a transfer," said Tuchel. "Everyone has their job to do."
The Bundesliga starts next week with Bayern facing Werder Bremen on August 18th.
The Bavarians, who won the league for a record 11th successive time last season, have been desperate to bring Kane in as they look to boost their attacking strength and battle for the Champions League title once more.
Kane, who joined Tottenham's academy aged 11 before making his senior debut in 2011, has not won any major domestic or international club titles in his career.
He has spent most of it at the North London club, scoring a club-record 280 goals for Spurs in over 430 appearances in all competitions, and 58 times for his country in 84 games, making him their all-time leading marksman.
He is also the second-highest Premier League scorer of all time with 213 goals - 47 behind Alan Shearer's tally.