The England international suffered the injury during his first training session after winning the Club World Cup on Tuesday.
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Colwill faces being sidelined for six-to-eight months as he recovers.
He was a near ever-present for Chelsea last season in the Premier League, starting 35 of their 38 matches in their successful run to qualify for the Champions League.
Ahead of tonight's preseason friendly with Bayer Leverkusen, manager Enzo Maresca admitted: "You know in our way, how important Levi has been.
"I spoke with him yesterday and I told him that if we achieve what we achieved last year, it is also because of him - and he was a main player for us."