The Blues will decide over the course of the next six weeks whether the player will require surgery on the injury.
Chilwell suffered the injury during the 4-0 win over Juventus in the Champions League in an innocuous incident, with Cesar Azpilicueta replacing the 24-year-old in the 71st minute.
“Ben Chilwell is out,” Tuchel confirmed. “He has a partial tear of his ACL, and the decision is to treat it conservatively. The next six weeks will tell the story if he makes it and be available or if he will need surgery.”
It is a crushing blow for the player, who had hit some of the best form of his career and become a key part of the Blues side that currently tops the Premier League.
Tuchel must now decide who will replace Chilwell in the coming weeks, with Marcos Alonso and Azpilicueta the obvious options starting with the home match against Manchester United on Sunday.
Despite the blow, Tuchel has revealed Chilwell is maintaining a positive outlook.
“We need to talk about it again in six weeks, maybe we don’t need to talk about it because everything is fine,” said Tuchel. “This is the best case, it does not help if we start now speaking about worst cases, because there is also a best-case scenario.
“The next weeks will determine the direction. Right now, this is what we have. There is never a good moment for big injuries, and injuries in general.
“This for him personally is a very bad moment, because he was so good and so full of confidence, he was a huge part of our performances and victories in recent weeks. It’s a shame and very sad.
“But he’s actually in the moment very positive, because his body reacted very positively to the first treatments and to the injury.
“So after a while you have to refocus, and focus on the positive things. And that’s now the next weeks to do everything possible he can to come back and help us on the pitch.”
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