The Championship club have replaced interim manager Neil Warnock with Leeds and Chelsea great Hasselbaink after an impressive spell as boss of Burton Albion.
The 43-year-old former Dutch international, who won League Two with the Brewers last season, has signed a rolling contract with the R's following Chris Ramsey's sacking last month.
The size of the task ahead for Hasselbaink has been brought sharply into focus by one of the club's favourite ever players Sinclair.
'Make Rangers great again'
The BBC pundit, who is a regular user of social networking site Twitter, wished the new Rangers boss well in West London and pleaded with him to bring back the glory days.
"Best of luck Jimmy Gloyd Hasselbaink, look after and make Queens Park Rangers great again. Pride of West London," Sinclair posted on Twitter.
Sinclair, who scored 16 goals in 168 games for the Loftus Road outfit - including THAT stunning bicycle kick - also had a warning for the club's players.
He added: "Jimmy Floyd is a top man. I just hope the QPR players are ready for hard hard graft."
Former goal machine needs to solve scoring problems
If Hasselbaink is to do that he must first find a way to inject more goals into his side.
Rangers have won the last two games 1-0 and a 0-0 draw before those was preceded by back-to-back 1-0 defeats.
It means Rangers find themselves 11th in the Championship table but just two points outside the play-off places.
Getting the Hoops back to the Premier League would go a long way to looking after and making QPR great again.
But given the competitive nature of the Championship it won't be easy.
Hasselbaink is already excited about the club's prospects telling BBC Sport: "QPR has an exciting feel about it".
"I feel that this is a club on the up," he added.
"This is an incredibly proud moment for me and I will give my all to represent the badge of the club."
Hasselbaink's first game in charge comes on Saturday when Burnley visit Loftus Road.