Chelsea have inserted a £35million release clause in the new contract signed by Ian Maatsen.
The left back signed a new contract when agreeing his loan to Borussia Dortmund for the season but his clause comes into play from June.
The defender made his debut for the Bundesliga side last weekend in a 3-0 victory against Darmstadt in which he started and played the entirety of the clash.
Maatsen, who joined Chelsea in 2018, made 15 appearances for Mauricio Pochettino's side this season but started just one Premier League fixture.
That came last month during a 2-1 victory against the Blues' London rivals Crystal Palace.
The 21-year-old found game time hard to come by despite an injury crisis that wreaked havoc on the Chelsea squad - particularly in the left back position.
The Blues will hope that increased playing time at the Westfalenstadion can aid his development or at the very least increase his market value.
Chelsea earned a hard-fought win in their last Premier League fixture against Fulham, which saw them climb to ninth place in the table, just three points behind West Ham in sixth.
Pochettino's side will attempt to overturn a 1-0 deficit against Middlesbrough in the second leg of the Carabao Cup semi-final when they return from their winter break later this month.
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