Ghana defender is set to make an injury return in March after being out for eight weeks with a fractured bone.
The Leicester City guardsman suffered a broken leg injury in the Foxes 1-1 draw with West Ham in October.
Despite being out with an injury, the former FC Copenhagen player extended his contract at the King Power stadium to 2022, following an impressive start to the campaign.
"I am very happy to sign this contract at Leicester City. I am a simple and easy guy. I work hard and I focus," the 23-year-old told LCFC TV.
"By God's grace, my recovery is getting better and I have to be strong when I come back. I have to be ready, for the club and for the manager."
Amartey joined Leicester from FC Copenhagen in January 2016 and featured five times during his first season as the Foxes won the Premier League title.
He has featured 64 times in total for Leicester, scoring his only goal for the club in the 2-2 draw with Stoke in December 2016.
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