The Brazilian full-back will spend the entire 2012/13 campaign at Loftus Road, where he will work under Reds legend and Rangers manager, Mark Hughes.
The news follows Monday's earlier announcement that Fabio's twin brother, Rafael, has extended his United contract until 2016.
Fabio has found first team opportunities limited in his Old Trafford career to date, thanks to misfortune with injuries and the tricky task of displacing Patrice Evra at left-back, but he has still made 53 appearances and scored twice.
His sustained run of involvement in the second half of the 2010/11 season culminated in a starting berth in the 2011 Champions League final defeat to Barcelona.
Sir Alex Ferguson is convinced the defender has the wherewithal to succeed at Old Trafford, however, having admitted in April: "I think a year out at a good level playing every week will make Fabio a real top player for us.”
More: Fabio profile | Rafael signs new contract | Tour 2012