"I'm looking forward to pulling on the R's shirt for the first time and giving my all for this club."
Chairman Gianni Paladini believes his signing shows that the club are determined to pull clear of relegation danger.
He said: "It's a tremendous signing for the club.
"Scott is a superb young player and we're delighted Chelsea have agreed to let him join us.
"With the backing of Flavio Briatore and Bernie Ecclestone we've been able to push on and this reiterates their desire to bring the best, young players in this country to the club.
"The fact Scott has chosen us over an array of other clubs in this division says so much about what we are trying to do here."