The Czech Republic international and 20-year-old Dutchman will be entrusted to Middlesbrough and Aitor Karanka next season.
Chelsea has agreed to send defenders Tomas Kalas and Nathan Ake on loan to Middlesbrough next season, Goal understands.
Czech Republic international Kalas impressed in 17 Championship appearances during a temporary spell at the Riverside Stadium last season, even as Aitor Karanka's men fell short against Norwich City in the playoff final at Wembley.
Ake, meanwhile, acquitted himself well for Reading in a brief stint last term, making five appearances in April to help the Royals maintain their Championship status.