Frustrated Newcastle coach Brian Smith says the Knights will have to work doubly hard to achieve anything this season because they simply cannot get a break from referees.

A depleted Knights side battled bravely before losing 16-13 to the Sharks at Toyota Stadium on Saturday night with two second-half penalty goals to winger Luke Covell proving the difference.

Smith praised his side for overcoming "setback after setback" although he would not single out referee Tony Archer for criticism or comment on the crucial second-half penalties.

However, he could not completely contain his frustration after another match in which he felt hard done by.

Asked if he thought the Knights, who have amazingly only won a penalty count twice in their 19 games this season, were due for a break in the second half by getting some calls go their way, Smith snapped: "No, no, we haven't had that at any stage, so I wasn't expecting it.

"Whatever we're going to get (this year) we're going to have to earn it and double earn it.

"Nothing's changed, it's just the same week after week so we'll just keep working hard for it."

A shining light from the loss for Smith was the NRL debut of Fijian winger Aku Uake, who earned a late start after Adam MacDougall was ruled out through injury.

The 20-year-old is a highly rated prospect for the Knights with former great Matthew Johns declaring he has the potential to be the next Lote Tuqiri.

Uake scored on debut, and was excellent in both defence and attack all night for Newcastle.

"Aku was outstanding I thought, he looked as if he thought he should be there," Smith said.

"He was dynamic and strong and confident.

"He's got some things to learn, but a very encouraging debut, I was very happy for him.

"He's been a very patient young fellow, working hard to become a professional player and he did it."

The loss was compounded by an injury to Knights halfback Jarrod Mullen, who is now in doubt for next week's clash with South Sydney after straining a hip flexor with 15 minutes to go on Saturday night.

"I'll have a bit of physio this week and see how I pull up at the end of the week, but it's pretty sore so it's not looking too good I don't think," Mullen said.

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