The defender, who rejoined Championship club Middlesbrough on loan last week, has committed his future to the Blues by signing a long-term deal at Stamford Bridge.
Chelsea youngster Tomas Kalas has put pen to paper on a new three-year contract at the club.
The central defender – who can also operate in a right-back role – has recently joined up with Middlesbrough on a season-long loan, having spent the 2014-15 campaign with the north east side.
Since joining from Sigma Olomouc in 2010, Kalas has made only two Premier League appearances for Chelsea – against Liverpool and Cardiff City respectively.
The 22-year-old has one senior international cap to his name, having featured in the Czech Republic’s 3-0 friendly win over Slovakia in November 2012.
Kalas, who has previously spent time on loan at Vitesse and Koln, will be hoping to catch the eye of Jose Mourinho as the Teessiders attempt to make another push for promotion, after play-off final disappointment against Norwich City in May.