The 21-year-old has made eight appearances for the Bees, in both defence and midfield, since initially moving to Griffin Park in November.
Sporting director Mark Warburton told Brentford's website: "We are delighted to secure Rob on loan until the end of the season.
"He is a player I have known from a young age.
"I have watched him grow technically, tactically and physically into a very consistent performer.
"He has a real appetite for the game, he is so keen to learn and he has huge development potential left in him.
"It is a pleasure to work with Rob and we look forward to some very good performances in the months ahead."