Mackie has been out since September with a hamstring injury, but the attacker is close to making a comeback.
Mackie was almost selected to play a part in QPR’s last match against Huddersfield Town, but Hasselbaink is determined to be cautious with the 30-year-old’s return from injury.
“Jamie Mackie is someone is so enthusiastic and full of life that we have to pull him back,” he said.
"He is training with the group and was very close to being on the bench today, but he has not played a match yet and has been out for 10 weeks, so it would have been a big risk for him.
"I would prefer him to play a few games first with the U21s, so that he is well conditioned as I can't afford to lose Jamie again for another 10 weeks.”
Mackie was brought back to QPR during the summer transfer window from Reading, but his start to his second spell at Loftus Road hasn’t gone according to plan so far.
The Scotland international has only played four times for QPR this season, and during those appearances he hasn’t scored.
Mackie’s impending return should increase QPR’s attacking threat though, and that will be a boost to the London outfit.
QPR have found wins hard to come by since Hasselbaink took charge, and they failed to win any of the Dutchman’s first five matches at the helm.
This poor run of results has seen Rangers slip down to 13th place in the Championship table, seven points away from the play off spaces.