FC Koln chief Jörg Schmadtke says circumstances have worked against Tomas Kalas this season.
The on-loan Chelsea defender has struggled for minutes since his August arrival and there is talk of him returning to London in January.
"It turned difficult for the boy.
"When he came to us, he was a little tired, then the coach has selected the best defensive unit. It's been difficult for him," said Schmadtke.
QPR are keen to takeover Kalas' loan for the second-half of the season.
