Bielsa lauds two Leeds signings who have overcome injury to become reliable performers for his side.
Koch had been playing with a knee injury since arriving from Freiburg in the summer.
The 27-year-old has agreed a four-year deal and will compete with Cooper and Koch for a starting spot.
The 27-year-old started his career at Real Madrid and moved to Sociedad in 2017.
The Real Sociedad star has a €50m release clause, but Leeds look set to land him on the cheap.
Liverpool legend John Barnes has picked out three players he would like to see at Anfield next season.
Liverpool are still weirdly desperate to sign a centre-half. They have three, all from La Liga, on their radar.