Chelsea have rewarded defender Andreas Christensen for his impressive return to Stamford Bridge with a new four-and-a-half-year contract running until 2022.

The Denmark international spent the last two seasons on loan at Borussia Monchengladbach in the Bundesliga and looked destined to become the latest Blues youngster to be cast aside for an inflated fee.

But the 21-year-old bucked the trend which has befallen dozens of Chelsea protégés by winning a place in the first team before becoming a vital component of Antonio Conte's first XI.

Christensen has made 22 appearances in all competitions for Chelsea season and has jumped above summer signing Antonio Rudiger and Brazil international David Luiz in the defensive pecking order.

Conte described Christensen as Chelsea's greatest surprise of the season last month and his form has earned him a new contract which should cement his status as a success story from the west Londoners' academy.

"This contract is reward for the excellent form Andreas has shown in the first half of the season," club director Marina Granovskaia. "He showed immense potential when he signed for Chelsea in 2012 and is now enjoying the benefits of the dedication and professionalism he has shown since.

"After two seasons on loan in Germany we were convinced he was ready to be a part of the squad this season and he has grasped the opportunity with both hands. We are delighted he has chosen to commit his future to Chelsea and we look forward to four-and-a-half more successful years with Andreas at the club."

The announcement is the latest made by Chelsea during the January transfer window, a period which has included two more young players leave on loan in the form of Ike Ugbo and Jake Clarke-Salter, who have moved to Milton Keynes Dons and Sunderland respectively.

Sixteen-year-old Austrian Thierno Ballo has meanwhile joined the club's youth ranks in an effort to emulate Christensen's success, yet the highest profile addition has seen Ross Barkley arrive from Everton for a reported £15m.

Andreas Christensen
Christensen has been one of the surprises of the season according to Antonio Conte. Getty Images