Middlesbrough are now leading the race to loan in-demand Chelsea striker Patrick Bamford, Goal understands.
After taking over at the Riverside Stadium last season, Karanka was quick to re-establish a working relationship with Mourinho, taking Nathaniel Chalobah and Kenneth Omeruo on loan for the second half of the Championship season.
Chelsea were pleased with how both players fared in the north east and that has seen them allow Omeruo to return to Middlesbrough - despite Premier League and top-flight interest from around Europe.
Newly promoted Leicester City, West Ham, Crystal Palace and West Brom are all understood to be keen on taking Bamford, along with Championship clubs Wolves, Brentford, Wigan and Derby, where he spent part of last season.
Bamford scored 22 goals last term over periods with MK Dons and Derby, and Chelsea are carefully considering their options for the next step in the 20-year-old's development - but Middlesbrough are in pole position.