Kalas completed a season-long loan-switch to Koln over the summer, but he has yet to make a single appearance in the Bundesliga.
The 21-year-old made two Premier League appearances for the Blues last season, whilst also appearing in the League Cup and Champions League, but his greatest triumph was in playing the full 90 minutes in the 2-0 victory over Liverpool at Anfield. Replacing the injured John Terry prior to the game, Kalas played a key part in Chelsea keeping a clean sheet against the free-scoring Merseyside club, and the once-capped Czech international was being tipped for a starting role following his performance.
However, the rejuvenation of club captain Terry - and the signing of Kurt Zouma from Saint-Etienne - further limited playing opportunities, and he moved away from the club until the end of the 2014/15 season.
It is his third loan spell away from the club, but both Chelsea and their player are said to be disappointed with the situation in Cologne, and QPR have been put on alert that the youngster may be returning to Stamford Bridge at the turn of the year.
As reported by the Mirror, Rangers could shore up their defensive frailties by loaning the player when he returns from Germany, with the option to play in the Premier League preferential to the 21-year-old defender.
However, it has been reported that any deal will likely be held off until the new year, as Kalas continues in his attempt to impose himself in the Koln squad, but Rangers will continue to track the youngster with hope of bringing him to Loftus Road in January.