Chelsea manager Frank Lampard has confirmed that midfielder Kai Havertz has tested positive for Covid-19.
As a result, the Germany international has entered self-isolation and was left out of Chelsea's team for their Champions League clash with Rennes on Wednesday.
Havertz will also miss Chelsea's match against Sheffield United on Saturday while he also appears likely to miss out on Germany's upcoming trio of matches as well.
Havertz moved to the Blues from Bayer Leverkusen for an initial fee of £70 million ($104m) in the summer transfer window.
Although he has managed four goals and three assists across his first 10 appearances for the Blues, Havertz has come in for some criticism over a perceived lack of influence in the final third. Three of Havertz's four goals thus far came in a single match – a 6-0 Carabao Cup thrashing of second-tier Barnsely in September.
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While Havertz has taken some time to adjust to the Premier League, his team-mate for club and country Timo Werner has backed the talented midfielder to eventually show his best form at Stamford Bridge.
“I know Kai very well and I think he is one of the most talented players in the whole world," the Chelsea striker said ahead of the match against Rennes.
"He is a young boy, only 21 and he can learn a lot but can already play like a very, very old and wise player. I think up until now he feels very well here.
"A bit like me, we have talked a lot about settling in and he feels he is very happy to be here. In a lot of games he has shown what he can do, what he can bring to the team.
"For Kai it is very important to score, but I think what you can see in his game, he is about a lot more than scoring goals as a midfield player. He plays a lot of key passes, makes a lot of movement for other players.
"He is very talented and feels good. He will get better and better, like me he has come to a new country, language and style of football and has to learn, but until now he plays very good and we will see a lot more good games from him.”