Charly Musonda will be with Chelsea until 2022 after signing a new deal with the Premier League champions.
The 21-year-old has become a fixture around Antonio Conte's first-team squad this season after making his debut on the opening day.
"I am very happy and very proud," he told Chelsea's official website.
"I came here very young and am very happy to continue my journey here. I love this club so it's a great moment for me and my family.
"Now I want to establish myself and progress into the team and stay here permanently."
The attacking midfielder spent the 2015-16 and 2016-17 seasons on loan with Real Betis.