Queens Park Rangers drew 0-0 with Nottingham Forest yesterday.
QPR could only draw 0-0 with Dougie Freedman’s side yesterday, with Washington saved until the closing stages of the match.
The new recruit entered the field with just over half an hour to play, but he could not score the winner for Rangers.
Hasselbaink was still impressed by the striker’s display, though, and the Dutch boss insists that he will only get better as he becomes more familiar with his new surroundings.
"Conor coming on and showing what he is about was a big positive,” Hasslebaink said.
“He will need time to settle here, but we intend to give him plenty of opportunities.
"I am confident he will be a big asset for us and I am encouraged by what I've seen from him in the short time he's been with us.”
Washington is QPR’s only signing of the January transfer window so far, and he has big boots to fill.
The former Newport County man has been brought in to help replace Charlie Austin, but he has been used sparingly so far.
Washington has been utilised as a substitute in both his appearances for QPR so far, with the front man also entering the field late on against Wolverhampton Wanderers last weekend.
QPR’s next fixture comes against Ipswich Town in two Saturdays’ time, and Washington could be in line to make his first start in the tie.