The 28-year-old has struggled to recreate the prolific form of his youth and a recent goal glut was undermined by a tortured display in the Club World Cup final loss to Corinthians.
Hasselbaink believes the former Liverpool striker can still get back to his best.
The Dutchman said: "I don't know - but why not? He just needs to believe in himself more.
"He is struggling a little bit with his confidence but that will only get better the more he scores.
"If he does, then I don't see why he couldn't get back to his Liverpool form.
"At least he is getting goals. He has got 12 so far.
"The only thing I can say is I would like to see him score more in 1-0s and 1-1s, those kind of goals. There are not enough deciders."