The German midfielder managed just one goal and four assists in 21 league appearances since arriving from Bayer Leverkusen for £71m.
Havertz, 21, was laid low by Covid-19 in November and was then used mostly as a substitute before picking up an injury last month. He believes he will start to show his best form now that he is fully fit.
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Chelsea’s Kai Havertz said he is now free of injury and illness and there can be no excuses if he fails to deliver at Stamford Bridge.
“The coronavirus is now over (for me) and I feel good,” Havertz told Chelsea’s website.